So about that Zenos' dream

[Cleretic]

My guess is that it would've been more important if the original plan of a Garlemald-focused expansion followed by a finale expansion had happened, but when both were condensed into Endwalker, it wasn't deemed important enough to make it.

Not plausible, at least not from the pacing we know.

We know from Ishikawa herself that the general skeleton of an expansion has to be done right around when the last one is released, to give the CGI trailer people appropriate lead time (they're apparently usually further along than that, but for Endwalker we know it was pretty close to the wire). This means that Theoretical All-Garlemald Expansion and Theoretical All-End-Of-Days Expansion were compressed into Endwalker before Shadowbringers, and so the vision from 5.2 was after that point. At that point they did know the framework of Endwalker, albeit probably not a textbox-by-textbox breakdown. The finalizing of the script and recordings happen around the .4 patch, so after .4 even that level of rewrite becomes implausible.

So if you want to claim that this was a dropped plot point it's not completely implausible at that stage, but it can't be from some lost expansion; it has to fit into what we got, somewhere. Maybe Zenos was at one point planned to be involved in Elpis, or more engaged with the End of Days events, which would've either given explanation to the dreams or given more purpose to the fact he had them?

Or maybe--and this is also completely plausible--it was always meant to be a minor beat with little to no explanation, that was just included so that Zenos has plausible knowledge of the End of Days so he's not just going 'what the hell is this nonsense' for the entire back half of the expansion. Not everything is a major plot hook, sometimes things just happen.