I want Victorian / Jack the Ripper era England but they've already previously announced that it will (unfortunately) never happen.
Well that's a shame I guess but they like to stay close to key historical moments, this one matches the French revolution so that fits into what they've always done. I'm waiting for something like WWI or WWII maybe?
Anyways, about how this game looks so good and still be called Alpha? I think the answer is easy, they've probably got a whole different team working on this for one, and they've probably started work on the engine targeting next-gen after AC3 was done, meaning for XB1 and PC this should be a full DX11 game. AC4, even if it's on the new systems is still the same old AC3 engine with some little tweaks, nothing new.