Yeah, Midna on the back of Wolf Link would've bee a great way to represent Twilight Princess... But, I'm less crazy about her and Wolf Link for two reasons, one, she's only been in the one game, and two, that's a fourth Link, hahahaa. I may be a little biased here though, Twilight Princess is one of the lesser 3D Zelda games in my opinion, and what I did love of it, was everything but Midna and the Twilight Realm... so, I'm kinda glad she's an Assist Trophy, sorry.
Tingle is interesting, but we know he's already a stage element for Termina Bay. And I get the feeling that'll be his role this time around. And I'm fine with that, he's a recurring dude in the series, but y'know, so is Skull Kid, and Skull Kid is much more of a major player to Majora's Mask too. I feel he'd have priority over Tingle and Midna.
...But not Impa. Impa is a really big deal in the series. Bigger than Skull Kid, for sure. And she was such a total boss in Skyward Sword too. A simple Echo would even do her justice, honestly. And of course the Zelda series is certainly popular enough to get a newcomer plus an echo. Like, that's even expected at this point, deservedly so.