I would say a new fire emblem for the wii no sequels or remakes a complete new game
however gba had 3 fire emblem games, gamecube has one I wouldn't be surprised if wii is only going to have one and ds ( including 3ds) will have 3+
but if it is indeed made for wii I think it should have...
fe9 style supports and a memory system so you can review them.
no laguz, but a few animal type fighters, like a manakete or maybe a wolf
new weapons/magic maybe ice/water or earth type magic
viewable growth rates after you beat the game, that way I don't have to look online and remember/review them.
high replay value, paths like in fe6 and 7 where if you did this or that you go to this or that.
I think there should be two+ different stories like in fe7 and you can choose what you want to start with in this one.
customizable lord, fe12 had a good idea but it doesn't seem like that great of a game I think it could be improved upon. I think it would be cool if instead of affinity characters had zodiac signs.
a final boss that makes you throw your controller in rage, I like games like that where the game has been easy/normal for the most part, hard for some parts and then WTF HARD! when you reach the final boss, but not too hard I don't want a final boss that's lolgheb hard.
well that's all my idea for now

maybe post some more if I think of something super awesome.