It's also important to remember that...

1. All we know is that an Ascian is involved, that's it. We don't know anything about their plans, and it would be wrong to assume it has anything to do with what they've done before (i.e. Rejoining, reviving Zodiark, wanting to destroy the world). Basically this Ascian or group of Ascians could have completely unique and interesting backgrounds/motivations that we don't know about. What we should be thinking about is how in any way would creating a massive Endless society be interesting to an Ascian.

2. It would be absurd to expect them to be shelved forever. Like it or no, the Ascians and the reflections are one of the main plot threads that are still hanging in the air, of course it's going to come back eventually. If anything, I'm glad they revealed it now instead of stalling and trying to surprise us later. Again, we know since 7.0 that whatever happened in the Storm Surge war it was orchestrated by an Asican (ok we didn't know know, but come on, it couldn't have been more clear) and since 7.2 we know that Calyx calls his reflection the Ninth, a nomenclature he could only have known by getting this information from an Ascian (according to Y'shtola in 7.0). So Ascians have been written all over this story.

Now, about the post credit scene...

1. Calyx was sweating and out of breath when he spawned in this unknown area, so does that mean that he managed to escape before we destroyed the terminal? And if not, then what the hell happened, did he have a backup and lied about it?
2. Calyx mentions "At long last, I was to open a new path!". A path to what?!
3. He also says he made rash decisions perhaps influenced by "the others and their developments" - I think this implies that the Winterers, whoever they are, seem to be getting desperate? Or maybe they're fighting amongst themselves? Tell me if I'm misinterpreting this line.
4. Assuming Calyx is still an endless, I think it's safe to say that he can only project his image somewhere that the terminal's signal can reach, meaning if his terminal in on the Ninth, he can only project himself on the Ninth (or the source, if the portal is open). Does that mean his meeting with this mysterious Ascian happened somewhere on the Ninth? Basically I think we can rule out them meeting at their usual place on the thirteenth.
5. This is a wild one but do you think "Winterer" could have anything to do with Blindfrost? We also had that line from Gossan "It's as if we were frozen in time, but now the ice has begun to thaw", could this also be a very subtle foreshadowing? If so we might be looking at a Blindfrost 8.0 expansion, truly fulfilling the Heavensward 2.0 prophecy. Again, this is wild speculation but I think it's fun.

Let me know what you think