> My understanding is that the FSF wants copyright assignment so that it can unilaterally determine its destiny. It can, for example, decide to begin releasing it under an entirely new license at some point. While it won't eradicate older versions under older licenses, it does make it easy to relicense the whole thing even if the original author didn't submit code with a "version X or later" clause.
Sorry, but this is BS.
The theory behind copyright assignment is that it's easier with litigations as you pointed later.
FSF could change GPL if they really wanted to, and the easy solution for authors that do not submit with a “or later” clause is to not accept such patches.