"If copyright does apply and the code is still in the code base, we can remove the contribution. Depending on whether current contributors and users still value the effect of that contribution, it may need to be reimplemented."

Will it sometimes be easier to just fork? Would fork-relicensing be a good thing for the community?

Or should there be a different approach to ownership that does not allow for relicensing?

As a contributor to some projects that relicensed, I felt pressured to accept a change that was packaged up together with some major downsides.