I feel like rewriting a GPL thing based on the GPL version should require the GPL licence. After all, you've built something on top of GPL code which means it's also GPL right?
If I go and build my own implimentation of GTK, how do I even prove that I made it entirely without looking at GTK because that's what's required to relicense right?
Solely from the fact that I'm telling you I made my own implementation of GTK, I'm admitting It's not clean room right?