Maybe the future is not that dark. It's not like they are a monopoly now and can rest and not innovate anymore. There's a lot of competition still. Arnold, and Fstorm and others.
If they would try to eliminate Corona in a few years, probably another rendering solution would pop up at some point.
Mixing the two in one single package would result maybe in a bloated and too complex plugin.
The only thing I would not like to see, is Corona becoming even simpler, focusing on good things like speed, but eliminating vfx oriented features. In order to not compete or overlap with Vray too much.