which sonic games are viable candidates for a multiplayer revival?

As an answer to your original question: I would love a Kirby Air Ride revival. The game was novel enough to keep my attention away from Mario Kart, and simple enough that any of my friends could play. And the City Trial and free run was great for just messing around for hours. Sonic Riders was good too for having a similar mechanic.

On the topic of 2-player sonic games: They're all kinda half-baked if there's a 2-player mode at all.
Sonic 2: 4 levels
Sonic 3: 3 small levels
SA2B: Easily the best 2-player mode. I spent hours (years) doing it but it's not great for competitive play.
Sonic Heroes: 3 levels that were about 25% of the actual levels' size
ShTH: 6 second of standing still and shooting each other until a random victor emerges
Sonic Colors: eh
And I think that's it for main games

The spin off multiplayer games are alright but none are great

 

Theres also Secret Rings which has some sort of party mode in it. Ive never played it though, ive heard its not bad

 

I entirely forgot that existed until you mentioned it. I never played it either.

I played a lot of Sonic 2 multiplayer, and I enjoyed it as a kid, but I didn't like that the winner passing the sign set off a countdown. It makes sense, but having never played with another sonic fan (or anyone who knew how to play video games as a kid), my opponents just got annoyed that they rarely ever got to finish a level.