Animal Crossing mobile needs to be something snappy enough like Pokemon Go, but also worthwhile to play for a long time (unlike Pokemon Go).
I expect it to be a game that'll imitate popular life simulators in Japan in order to get max profits.
As for timed exclusivity, I never understood the appeal. Unless Nintendo is gaining ridiculous money to keep a game hostage, I think it'd be more worth it to release it on both platforms. Just look at Super Mario Run. The game isn't even released on Google and it's dead...