In terms of fan service, I could see Midna become playable in Age of Calamity through DLC. A campaign around the Mirror of Twilight could be a thing honestly.
Also it's the anniversary of Zelda next year. I do expect a Zelda newcomer as DLC, as the very last character in fact. But to be honest, I think Impa has the edge...
I definitly wish, it would be awesome to see BOTW styled Midna in the game, especially since ... For now ... The roster looks pretty dissapointing in that game TBH
As for Impa having the edge, I really dunno, Impa is a recurent character for sure, but .. In all the time she appears, she's a very side character, honestly I'm not sure that Impa would be as remembered as Ghirahim or Fi if her only apperance was in SS for exemple, or as remembered as Darunia, Sheik or Ruto if OOT was her only one, if you see what I mean
Even in the new AoC, people do a big deal about Impaya, but, from what we saw so far ... She really don't have that much importances in the game at all .. Even the mission where she meet Link just had her tripping over in a cutscene to give Link the Sheikah Slate, and .. That's pretty much it, in other cutscenes we saw her appear in, she's just loosely in the back, not saying anything, so I'm not entirely sure it gives her the edge
Especially since if we count Hyrule Warriors games, then it's only fair to count the first one, which definitly give Midna an edge for being important to both the first game's scenario, and the second (Only one of the HW's Wii U DLC to get a custom scenario in Legends I believe ?), as well as .. Well, having two spots on the roster instead of one, which is something only Links and Zeldas have apart from her haha
HW Impa was also a bit more important to the overall story, and people definitly like her, but I dunno if it primes over Midna, I would say they have pretty even chances myself, it's not like Midna is old news either due to TP HD
... I can see the AT being a problem TBH, which may be a reason that would bother her chances, but honestly, work arounds exists for AT, so if they really wanna put Midna, they will
I dunno, maybe I'm a bit too optimistic about all of this, but I honestly don't see Impa having an "higher status" than Midna