[isilofi]

The important distinction isn't who owns copyright. It is rather that there needs to be a community opposed to the license change and able and willing to do the work.

One could even imagine scenarios like an originally MIT-licensed software splitting into a commercial company offering commercial paid licenses, plus a community (or even the company itself) offering a GPL-licensed fork. Of course one could then still maintain an additional MIT-licensed fork, but if the rest of the community is happy with GPL and all the development just happens there, your MIT fork will "starve"...