Sometimes, it just takes sweet irony to get the job done. During Unleashed's development, all they did was simply look back towards Secret Rings, borrowed some of it's gameplay elements, and threw in Sonic's now-signature boost from the Rush games to add extra flavor for the daytime stages. This in the end came Colors, which in turn continued towards Generations, which further improved Modern Sonic's gameplay mechanic, which was heavily borrowed from Unleashed.
If Sonic can do that then Mega Man can do the same. We have Rush Marine, yes? We could have Classic Mega branch off into a shoot 'em up based on that engine while X can bridge the gap to the Zero series with the Command Mission RPGs, completing the circle.