The rift, the crystal tower, and the seat of sacrifice (Spoilers up to 6.0)

[Iscah]

The way it seems to me, time travel within the same Shard doesn't work, because you can't change the past. This includes going back to the pre-Sundering era, because it's still technically the past of the same Shard. But jumping to another Shard changes the variables enough to break the time stream, or at least create an alternate one.

To use a (probably bad) metaphor; traveling back in your own past, like Alexander, is just riding the train back along the tracks. It can only go one way. Jumping across the Rift and traveling through time is diverting the train onto a new set of tracks.

That's not how it works, though. All the shards together are in a single stream of time, and their fates are entwined. You have the 8UE timeline where the First was rejoined and its aether wrecked the Source, and our timeline where they remain separate. There's a copy of all the shards (or what is left of them) in each stream.

[Cleretic]

The way it seems to me, time travel within the same Shard doesn't work, because you can't change the past. This includes going back to the pre-Sundering era, because it's still technically the past of the same Shard. But jumping to another Shard changes the variables enough to break the time stream, or at least create an alternate one.

To use a (probably bad) metaphor; traveling back in your own past, like Alexander, is just riding the train back along the tracks. It can only go one way. Jumping across the Rift and traveling through time is diverting the train onto a new set of tracks.

While I don't necessarily agree with this, I do think it's interesting to consider, because we don't know that's not how it works. We don't know the actual rules of time travel in this universe, we just have multiple instances of time travel that we know worked and happened, and just have to work from that. The only one that knew how time travel works was Alexander, and it ain't talking.

Maybe you're right, and it's not what you do after time travelling that determines if the timeline forks or loops, but how diagonal the time travel route was. We don't know, and nobody in-universe (at least, who's still an operating part of the timestream) knows, because nobody was actually present for all four major time travel schemes; the WoL and Y'shtola were near all of them, but Y'shtola participated in none and the WoL was only knowingly involved in one (their level of involvement in Alexander's greater time loop is very debatable).

[Jandor]

Simplest explanation for me is that the crystal tower took a chunk of the Source with it when it left, and that chunk is what forms the 8UC world, which hurtles along the same overall timeline as the rest of the worlds that make up Etheirys.

One big overall timeline, one big overall closed loop time travel story.

[Iscah]

Simplest explanation for me is that the crystal tower took a chunk of the Source with it when it left, and that chunk is what forms the 8UC world, which hurtles along the same overall timeline as the rest of the worlds that make up Etheirys.

One big overall timeline, one big overall closed loop time travel story.

I don't know quite what you're picturing but it sounds far more convoluted than a split timeline.

Which "chunk" of the Source? What did it attach to instead? What caused the calamity if it exists in the same set of dimensions as the still-unjoined First?

[Necrotica]

Simplest explanation for me is that the crystal tower took a chunk of the Source with it when it left, and that chunk is what forms the 8UC world, which hurtles along the same overall timeline as the rest of the worlds that make up Etheirys.

One big overall timeline, one big overall closed loop time travel story.

This makes sense to me actually. It is not so much an entirely separate timeline. But a preserved chunk of one. A bizarre time capsule.

[Lyth]

You can theoretically use time travel to change events on the same shard. As the perfect machine, Alexander calculated out the end result of every possible timeline in which it could intervene, including one in which it went back and prevented the Seventh Umbral Calamity. The main reason why it chose not to alter any part of the timeline was because its aether upkeep always made it a risk to the planet in the long run. It also realized, through its encounters with the player character, that they were going to sort everything out anyhow. So the only alteration that it made was to construct a time loop using Shanoa that effectively removed it from ever being used. Alexander always had the option to alter the past, present, or future however it saw fit; it's judgement was not to because of the consequences of those alterations, having seen every such timeline.

[Kranel_San]

You can theoretically use time travel to change events on the same shard. As the perfect machine, Alexander calculated out the end result of every possible timeline in which it could intervene, including one in which it went back and prevented the Seventh Umbral Calamity. The main reason why it chose not to alter any part of the timeline was because its aether upkeep always made it a risk to the planet in the long run. It also realized, through its encounters with the player character, that they were going to sort everything out anyhow. So the only alteration that it made was to construct a time loop using Shanoa that effectively removed it from ever being used. Alexander always had the option to alter the past, present, or future however it saw fit; it's judgement was not to because of the consequences of those alterations, having seen every such timeline.

I really dislike how one of the possibly strongest primals to ever exist is just a side quest summon and not integrated into the MSQ..

[Cleretic]

I really dislike how one of the possibly strongest primals to ever exist is just a side quest summon and not integrated into the MSQ..

Look, I'd be on board with making Alexander MSQ-mandatory, but that sort of decision is not historically popular.

It's absolutely fine for side content to be 'big' stories in their own right, because if you only let the MSQ-relevant story arcs be large-scale then you run the risk of everything feeling unimportant by comparison. That's not to say every story needs to be of that scale, but it's both hindering creativity to say side content can't be, and cutting out people (of which I've met plenty) who are only interested in that large-scale stuff.

[Lyth]

I think you're better off thinking of FFXIV's story as modular. The MSQ is designed to keep you up to date with the essential plot events while getting you into the gameplay. It's already fairly cutscene heavy, so if you added more story content to it, people will get overloaded with information and will be more likely to skip through it. That's why the Unending Codex was likely added, to give such players an easy way of understanding the core plot without having to remember a lot of additional details. If the story is really important to you, however, none of the 8p raids are really 'optional' or 'side content', and all of them end up having tie ins to the MSQ in the long run.

If you think that missing the Alexander storyline is bad, both the Coil and Eden stories have an even bigger impact on the plot. Coil has hidden away a major cutscene explaining the true events of the Seventh Umbral Calamity, and Eden has a significant amount of lore about the First, Thirteenth, and the Ascians, including some fairly interesting commentary on utopias from Mitron that sets up the main themes of Endwalker. Not only that, but the many of the boss designs and mechanics have subtle bits of lore behind them as well, such as Cylva's sword in E10S, E11S's boss design as a curious hybrid of Ran'jit and Thancred, and the Savage-exclusive second phase fight against Loghrif in her true form that references your earlier fight against her in E2S as well. If you're at all interested in Void magic, it's a pretty amazing series. And to think that Pandaemonium is likely going to be even bigger than this in terms of lore impact.

In short, it's all important! The only thing that I can say is truly 'side-content' is when you try to clean out random '!' marks from your map, but you can find surprises lurking there as well.

[Cleretic]

And to think that Pandaemonium is likely going to be even bigger than this in terms of lore impact.

I completely agree with the rest of your post, but this part... no, I really don't think so. Not saying Pandaemonium's not gonna take some wild turns and give us one hell of an origin story for at least one fairly major villain, but I don't think Pandaemonium's gonna have a huge lore impact. If nothing else, it's got a huge problem of distance; it's basically as far away from the core events of the game as it's possible to get; it's gonna be real hard to drop impactful lore bombs on the game's present day from twelve thousand years in the past.

Granted, they still managed to do a bit of that in the main story, so I wouldn't be too surprised, but I'd be surprised if the impact of Pandaemonium on the present-day setting is anything more than 'now you have an origin story for the namazu, and a sad backstory for Lahabrea and/or Elidibus'.