It's a shame, because the tone of X-Com 2
should be obvious, and was nailed by a fan trailer:
foreign to our own homeworld. Erasing the human from humanity, and such.
It's something that's harder to nail down with little things or with only being able to look at missions. The ultimate goal to not use humanity as slaves but literally kill us all to create Avatars is also a problem for it. They have no reason to oppose human-ness, since we'll all be dead instead of a slave race like the others.
If there does end up being an X-Com 3, I'm afraid for it. I want to say there is no way they'd try to "reset" again and do the same formula, but they did do it once, and quite literally. This is especially an issue as X-Com 3 could be great as an Earth vs. the Galaxy game. You saved the homeworld, good job, now there's only a hundred billion stars left.
So your small force becomes Earth instead of X-Com, and your large force becomes the Alien Empires. Galaxyscape instead of Geoscape, space combat instead of air combat. You can't really take down the whole alien empires, and that isn't your actual goal either. Your goal is to carve out a place for humanity that can survive.
Start off incredibly bleak - maybe the Ethereals are the largest force or maybe they are not, but
everyone is hostile to humanity because of how weak we are. You have to establish a human region of space, you have to fight off alien incursions, you have to destabilize some empires and make lasting peace with others. X-Com remains what it is, a special forces group that strikes at critical targets to make this all happen.
It'd be a fairly different game than what we're used to but that's fine, progression is what the story needs.
More likely they'll just reset again, but hopefully that takes the form of something like "the extradimensional nightmare machines the Ethereals are running from are here and they're hungry, of course your tech isn't enough it wasn't enough for the Ethereals either".