I would really love a TP sequel. I think it would have to be very different from TP or any Zelda game before, though, especially with all the new potential unlocked by the Wii.
Exploring the potential of Wolf Link more would be great. Of course, to do that you would need to bring Midna and/or the Twilight back, which I would have no problem with. However, if Midna wasn't there (perhaps in need of rescue, if twilight returned...?) it would offer more chance for character development of Zelda. She had really very little role in the game, which I found rather disappointing. (See my post in the Game Where You Actually Play As Zelda Thread...) If Zelda was playable, I think it would be very interesting and challenging for her to have a completely different fighting style. After all, she has a rapier, which you would not use at all like you use a longsword. She also has her bow and arrows, as well as her magic.
Speaking of which, there should be magic. We all know that Hylians are supposedly the best at magic--and yet I can think of one time when I have seen a Hylain use magic of their own. In Japan, LOZ was released as Hyrule Fantasy, I think, so it would make sense for it to be more fantasy-like, if only based on this.
I also thought that the Twilight Realm made no sense. You call three buildings floating in the sky a realm? If twilight returns, then I think the Twilight Realm should be expanded and explored deeper. Perhaps beneath the Palace there is level upon level of shadowy city, rising up into the dusky sky...

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Let fear be cast into the hearts of our enemy. Let them lose all hope and let their heart sink into the unending darkness. Let them have no will to live. Let them feel the power of the Sages of Despair! (The Watcher-in-the-Night remains loyal!)