A delay to February would be fine. I'll likely pick it up whenever it's released, but it's easy to see it getting lost if it comes out in the wake of Mario Odyssey. It's also entirely possible Nintendo have another release that could come out in December. Possibly Smash Brothers, but I'd say Pokken in September after Arms in June is enough: but I expect it's also the case Nintendo are bringing out titles with online multiplayer to increase the number of subscribers starting in January 2018.
Anyway, I can see this game finishing development this year. A lot of people saying Monolith Soft couldn't possibly have made the game in two years are ignoring the fact X took so long because of it being Monolith Soft's first HD game, and because of online features. Monolith Soft needed to make new development tools and learn new skills, and make the game engine, and needed Nintendo's help with online. XC2 is almost certainly re-using the game engine made for X, as well as the development tools, which will help cut down development time.
Like I said, February would be fine. I just wonder if there's another title being pushed into the December slot.