I'm not saying this is a good idea (it is not, please don't do this to your open source community of choice!) but it'd be a pretty funny use of copyright licens

I'm not saying this is a good idea (it is not, please don't do this to your open source community of choice!) but it'd be a pretty funny use of copyright licensing to reserve all rights on the non-GIL improvements unless the GIL ones were also merged. Strong-arming an open source project with sheer programming skill.