Yes, I suppose they would have to back up time and take an earlier branch where the number of significant contributors was much smaller and easier to cull down.
If they wanted to do that there's no need to get an ok from 100 or so devs, because you only need a working version, not to be able to use avery single release with the new license. VLC was able to do it (albeit the change was from gpl to lgpl), there's probably 10 or so devs that owns 80% or so percent of the copyrighted code from the current version, once you get those to agree with the change, in the worst case you have to rewrite 20% of your software.