If he wanted to switch to GPL, he wouldn't have to relicence all the code; just the code that is by him alone. The contributions by others are in a permissive l

If he wanted to switch to GPL, he wouldn't have to relicence all the code; just the code that is by him alone. The contributions by others are in a permissive license that is compatible with the GPL, so they could remain in their current state; but the whole project would contain GPL code so anyone redistributing the project would have to do abide with the terms of the GPL.