I can see Animal Crossing being an "earn it or buy it" or a strictly "buy it" model.
The game works like every other Animal Crossing in that the store stock rotates and changes and you can find random stuff, but there'll be a real money store where you can buy whatever you want. Or you can buy in-game currency (Bells or maybe even DLC-exclusive currency).
Alternatively, it could go the Sims route and have a nice, built-in set of stuff, but with tons and tons of extras you can buy for real money. I'd like to think that the game will be perfectly playable for free, preying on the wallets of "collectors", "completionists", and the impatient for its profits.
As for Fire Emblem, I'm working my way through Awakenings right now and there's quite a lot of DLC stuff in it...I'd imagine they'll expand that idea with maps and characters, maybe a special item shop and such.