I don't know why you're under the impression that Teddy becoming Captain Marvel would HAVE to mean Carol loses the name. Haven't you been following Marvel Comics lately? It's all about sharing the mantle these days.
Billy as Sorcerer Supreme is something I would've loved years ago, but now? Who needs a Sorcerer Supreme title when you're destined to be the Demiurge, literal god of the multiverse? Strange can keep his title.
And I agree that Eli is not likely to return, but not because of the new guy. Rather because some **** went down with the Bradley family and they seem to be banned from comics.
I like your ideas VERY. MUCH. Jonas as the ''Friday'' of the Young Avengers would be GOLD. And you know what I just thought? What if that body Vision was building at the end of The Vision was not Vin or Virginia, but rather a new body for Jonas? BOOM! Unlikely, I know, but it would be a cool twist. I liked Jonas and I miss him.
And yeah, I definitely want more pre-Kang Nate Richards. I don't need him to be a hero and ally again, but I would like to know more about him and how exactly he went from young hero to one of the most vicious Avengers villains ever. It would be cool to have an arc where that is explored.
Oh, and I just had a super random thought: if we were to have an Iron Lad on the Young Avengers again who's not Nate Richards, I would like it to be Arno Stark. No specific reason, I just think it'd be a cool way to use the character again.