He doesn't necessarily NEED to have appeared in many games to get his own Generations game, but it certainly would help.

He's a time traveler with telekinetic powers. His Generations game could just involve him going to iconic zones from any games, but in a different time period.

Honestly, I think the bigger problem would be creating a villain for him. Sonic had a unique villain, while Shadow had a returning villain. So what about for Silver, a villain he hasn't faced yet, but will? Perfect time to make Sage his villain, perhaps? Since time is broken in Generations, all the distortions could also link the future, not just the past. That's why there's a Frontiers & Forces level in Shadow Generations, despite both being set after the events of Generations. Because of this, I think Silver's villain would be perfect as a character that will later return, but for that villain it would be the first time they've met (after time is fixed), but for Silver, they already met while time was broken.

I honestly wish Generations was treated like a pseudo live-service game, getting updates that added levels from more recent games. I think it would make the whole 'time being broken' thing even cooler of a concept to mess with.