POSSIBLE PRIMAL

[Sigiria]

Here's the full list of the remaining summons that appeared in other FF but did not make an appearance in any form in the XIV yet

Asura [FFIV]
Remora [FFV]
Crusader [FFVI]
Maduin [FFVI]
Raiden [FFVI]
Seraph [FFVI]
Tritoch/Valigarmanda [FFVI]
Quetzalli/Palidor [FFVI]
Ragnarok [FFVI]
Hades [FFVII]
Brothers [FFVIII]
Doomtrain [FFVIII]
Eden [FFVIII]
Quezacolt [FFVIII]
Pandemona [FFVIII]
Madeen [FFIX]
Valefor [FFX]
Anima [FFX]
Magus Sisters [FFX]
Mateus [FFXII]
Adrammelech [FFXII]
Zalera [FFXII]
Shemhazai [FFXII]
Hashmal [FFXII]
Zeromus [FFXII]
Exodus [FFXII]
Famfrit [FFXII]
Chaos [FFXII]
Ultima [FFXII]

All of these only appeared in a single main FF so at that point wouldn't be suprising if they ended showing up as simple bosses.
I'd see the next trials being Byakko, Genbu, Suzaku and Soryu. just because they appear on the map around kugane

[Arutan]

Everyone consider Magus Sister from FFX even tho they're originally from FFIV

[Sigiria]

Everyone consider Magus Sister from FFX even tho they're originally from FFIV

In FFIV they weren't a summon but three humans bosses. So the summon refer as the X, the same way if I refered the summon tonberry I would say it's from FFVIII even though tonberry existed before that as monsters

[Arutan]

In FFIV they weren't a summon but three humans bosses. So the summon refer as the X, the same way if I refered the summon tonberry I would say it's from FFVIII even though tonberry existed before that as monsters

Yeah but as someone said just above

They've added the Warring Triad who aren't summons in the past but are made Primals here so there's always that possibility they'll add Primals that weren't summons previously.

[Ultimatecalibur]

Crusader [FFVI]

Crusader/Jihad already appeared in the form of its individual components when we faced the Warring Triad as the Crusader Magicite was implied to be a fragment of the triad's power. Though it would be cool to fight them together in their Crusader forms as part of a 24 man raid.