Guessing Derplander's job next expansion.

[Ramesses]

That fancy Nero armour is just Warrior gear though, the poses match it.

The armour or pose is inconsequential... its the weapon that I'm more concerned about. That gunhammer is called Mjolnir and he designed it himself.

[gumas]

I say its that class with the gunblade.

Or BLM

[Iscah]

The only place we're going to in 5.0 is the psych ward. The Scions are going to stage an intervention to deal with the Warrior of Light's addiction to glamour prisms and Fantasia.

Guys? Guys? I just had this really strange vision. I know the nice man in the white coat is helping us deal with our memory loss due to overexposure to reality-warping crystals and all, but I think... I think we're supposed to be saving the world? There was a light and a giant crystal and it spoke to me and.... no, that's just the glamour prisms causing hallucinations again? oh...

[Ramesses]

I say its that class with the gunblade.

Or BLM

BLM...? Blackmage...?

[Zohar_Lahar]

It will be Ceruleum Mage, the new gunblade tank that involves using monster skills.

[Rhomagus]

While folks are guessing classes they hope it will be, I think it might be in our best interest to do our best at eliminating jobs then choosing from what's left over.

Before we can do that first we must establish a pattern and purpose for why Derplander has donned the roles that he has:

Why was Derplander a Dragoon in the Heavensward trailer? Why did they choose Monk to be Derplander's class in the start of the Stormblood trailer? What jobs were left to show and why didn't they choose any of those before the Derplander was depicted as a Samurai in the latter parts of the Stormblood trailer? Why did they not choose a multitude of other classes?

So to go with our first question, Why Dragoon for Heavensward?

1.) Thematically Ishgard is at war with dragons and Dragoons are from Ishgard.
2.) Of the jobs depicted in the fall of Dalamud trailer only Dragoon and Monk were not presently shown. Jobs depicted in CG form at the time (WAR, PLD, BRD, BLM, WHM,)
3.) Arcanist and SMN were not in the game at the end of version 1.0 so it wasn't considered a "missing" class/job. They could've used it to sell ARR, but perhaps didn't have the final touches done to the job to give to Visual Works (the company responsible for SE's CG animation)

Onto the second question; Why choose Monk for the opening for Stormblood?

1.) Thematically we're going to Ala Mhigo and Monks had already been confirmed to have been originated from the Fists of Rhalgr, a Monk group.
2.) Monk was one of the original jobs from 1.0 yet to be depicted in CG form. (WAR, PLD, DRG, BRD, WHM, BLM)
3.) While SMN could've been depicted, thematically Monk takes precedence due to missing from the original seven jobs, so it's time has finally come for Stormblood.

Onto the third part of questions. Why Samurai?

1.) Thematically we're also traveling from Eorzea to the Eastern themed Doma.
2.) A wonderful opportunity to showcase a new job that also matches thematically to the region being depicted.
3.) Ninja could've been depicted, but it's already depicted by Yugiri later to close out the trailer.
4.) You would think this would eliminate Samurai from the choosing as Gosetsu is also depicted.
5.) Still no Summoner? Would have been a fine opportunity, but it seems clear that the marketing team felt it better to highlight the Eastern themed Samurai.

Last question. Why not the other jobs?

1.) SMN, NIN, DRK, AST, and MCH were jobs already in the game. Why didn't they choose any of them? Likely due to them not finalizing their Artifact sets, or they were already depicted (NIN).
2.) The jobs excluding NIN weren't thematically consistent with the expansion. (Ala Mihgo for Monk, Samurai for new job showcase and Eastern theme)
3.) Why didn't they choose Red Mage if Samurai was already depicted in the end of the trailer? Probably because Red Mage has no thematic tie to the expansion.
4.) Why wasn't Summoner chosen then? Similar reasons. Thematic consistency trumps new job showcase or "it's the job's turn to be CG'd" (possible reasons for DRG and MNK)

So with all of these qualifiers taken into account we can make a list of least probable to be depicted. Let's start with job that have already been featured in some for or another in a CG trailer:

1.) Warrior - already depicted (ARR)
2.) Paladin - already depicted (ARR)
3.) Dragoon - already depicted (HW)
4.) Monk - already depicted (SB)
5.) Ninja - already depicted (SB)
7.) Samurai - already depicted (SB)
8.) Bard - already depicted (ARR)
9.) White Mage - already depicted (ARR)
10.) Black Mage - already depicted (ARR)

In order to give the new trailer the best chance at creating a spectacle at Fanfest, it would be best to choose a job that is both thematically related (HW and SB) and/or newly introduced (SAM for SB). Of the jobs we have available to us after eliminating the above we can make a new list to which we can begin to whittle down to a best possible candidate. The known jobs left are:

11.) Summoner (time is due, but thematically relevant to the area?)
12.) Scholar (see Summoner)
13.) Red Mage (Thematically relevant?)
14.) Dark Knight (Thematically relevant? With "Shadowhunters" being a possible title... perhaps? Not a bad choice)
15.) Machinist (Thematically relevant? Garlemald being a highly speculated area to be explored in the expansion and Garlemald's reliance on tech makes this also a good choice)
16.) Astrologian (Brave choice. Lacking the basic actionable scenario's that would make the trailer an action packed spectacle. Though AST LB3 is GORGEOUS!!! Brave choice. Certainly not a conservative estimate)

With Stormblood we had the introduction of two new jobs. Some popular speculations for the new expansion include the following:

17.) Blue Mage (Thavnairian theme? Ceruleum/Tech theme?)
18.) Dancer (Another nod to Thavnair. A lot of people screaming for Dancer ever since Lyse was shown in the SB opening. This would certainly excite and assuage those who were let down by Lyse only being a MNK.)
19.) Soldier*/Commando*/Gunblade/Magitek Knight/??? (Yoshida and the development team have been hankering to create an XIV specific job. A true mark on the franchise as a whole to which the XIV team could use to leave their indelible mark.)

The Heavensward and Stormblood depictions filled the original ARR jobs gap by filling in both Monk and Dragoon. Jobs that were left for wanting by the community for their lack of depiction in the ARR opening. These trailers also helped establish the importance of theme in order to show off the tone and setting of their respective expansions. With this being said, I would like to finally submit the possible jobs that will be depicted and why I think they are most likely. I'd wager that, like the Stormblood opening, we'll be introduced to a fresh new look to a job in which we're already familiar. Derplander will start as an already familiar job and gradually transform into one or two new jobs throughout the rest of the trailer. Either Derplander will don all depictions or Deplander will only don the garb of two jobs and the possible third job will be depicted by someone sharing the screen with Derplander. With this in mind, I surmise that Derplander will open the scene as a Machinist fighting off Garleans using Eorzea's best interpretation of Garlean tech available to them, but he'll be ultimately dispatched and saved by someone else who also utilizes the power of the enemy. A more natural enemy, not a technological one. This person will be a Thavnairian trader, face hidden behind the turban and mask of a Blue Mage who will eventually smuggle Derplander behind enemy lines through a Thavnairian trade vessel. Upon arrival, we're met by a stronger enemy than the Empire itself, and though reluctantly, only by joining forces with Garlean rebels are we able to save Eorzea, by saving the nation state of Garlemald itself. The theme of 5.0 will be all about becoming our enemy in order to defeat a more dire threat and a synthesis of technology and more traditional means of battle will be synthesized together in order to defeat said threat. Before the trailer fades, the Warrior of Light reaches for a Gunblade and leads the charge into another Carteneauesque epic battle of a Rebel Garlean/Eorzean/Doman alliance versus the Ascians and their army of Voidsent, ushering in the twilight that will drop the curtain on a realm reborn.

*class names that already have history in the franchise

[Bhearil]

I agree that of the current jobs imo Machinist is the more likely considering its ties with Garlemand tech (even if its been modified to use aether as well)

[XykeVayaris]

Someone give OP a cookie

[Duskane]

Winner goes to Dark knight

[Enkidoh]

Watching the teaser trailer again, it makes perfect sense that he not only cycles through different Jobs, that he eventually ends up DRK, because of what he is fighting against in that trailer. Ignoring the whole 'you must become the Warrior of Darkness' spiel for now, he became a DRK simply to counter the kirubu, as everything else he threw at it the stupid Amdaporian construct no-selled. Watch the scene closely - he's struggling to fight it and it just swats him away (it actually breaks his weapon when he becomes DRG!). And, remembering back to the level 70 SCH Job quest and Lost City of Amdapor HM, what elemental alignment did the Amdapori specialise in (and which their constructs like Kiburu were powered by)? Light. And what is Light's elemental opposite? Darkness.

So it made sense in a logical way - he bcame DRK simply for pragmatic reasons, reasons which I'm sure will be given greater clarification and context by the complete trailer next year just prior to Shadowbringers's launch date.