Also:
How's tech gonna work in this game. I mean, this is set after XCom1.
Something which kinda went under the radar: It appears there are actually melee attacks now. Which gives a lot more potential for classes. I can easily see an 'Assassin' or 'Infiltrator' class. Especially when you remember Ghost Armor.
And as for Earth being under alien control; the Sectoids have either managed to evolve very quickly or the Etherials have upgraded them even more drastically than they had tried to already.
I get the feeling something happened after the 'test'. Perhaps after Earth passed the 'Test' the main group came or hell; they made a peaceful integration. I mean, note how you don't see any of the old aliens in the clip. You see snake-men and Sectoid V2... who sticks to the shadows, and most people never saw an Ethereal, so perhaps them showing up [Possibly mind-controlling the Council] and offering to uplift humanity and repair the damage done by their 'enemy aliens' or whatever worked. It also doesn't say 'defeat' 'invasion' or so on. It says 'unification'. I dunno about you; but 'Unification' sounds peaceful. And the Aliens don't seem to be acting tyrannical or harming civilians, they are looking for resistance... which is XCom. Who show up. Showing their searches are perfectly founded.
I doubt the canon is 'XCom failed'. Firstly; they say 'Welcome back Commander'; implying XCom 1 did happen. Secondly if XCom fails the entire project is dissolved. So there wouldn't be an XCom for you to return to.
There are a lot of questions, and not a lot of answers :/