Realistically, there are probably dozens of titles that Nintendo could publish that would both be exciting as well as being considered the "deep end" ... For example, back when Nintendo announced Animal Forest + (Animal Crossing) was being released on the Gamecube in North America they mentioned that it was their largest localization effort ever. It was such a large effort because it had more in game text than any Nintendo game before it, and they also had to add/change content because of differences in holidays (and what not).
The other thing that needs to be considered is that I (and other people) have been wondering what a lot of Nintendo's studios are up to being that Nintendo has released less Wii and DS games than their studios have the capacity to produce. Now, I don't want to suggest any conspiracy theories but, it is possible that Nintendo has finished development of an exciting game that has yet to be announced and are waiting to release it (for some reason); theoritically, it could be a game which might be dependant on Wii MotionPlus and (until that is released) they can't release the game.
