We know for a fact that the Sonic the Hedgehog movie is getting a sequel, and there's a pretty good chance Tails will have some time in the spotlight. That said, it seems another big Sonic character will be getting some love as well.
Rumors are floating around concerning Knuckles, who will supposedly have a notable role in the sequel. This is going to be considerably more than a cameo, although details haven't been shared. It does seem that Knuckles gliding and wall-climbing abilities will be showcased as well.