Doesn't this clause seems not backwards compatible with GPLv2? At face value GPLv3 seems more constrained - so it's easy to relicense an existing v2 project. You just tell everyone working on it, okay, now every addition we make has extra requirements (if you want the looser version, you can grab an older copy of our project from when we switched licenses) Loosening the license on pre-existing code is sorta like if y…
No, GPLv3 and v2 have always been incompatible. v2 forbids placing additional restrictions on distribution, whereas v3 adds more requirements (e.g. patent grants). So if you receive code under v2, you can't distribute it under v3, nor can you distribute v3 under v2, nor can you combine them.