The real problem is what this means for upstream developers. If the language incompatibilities are mostly cosmetic then downstream distributors will be able to hold a transitional patchset together without the upstream developers having to branch, upstream can just make the move to py3k and the cosmetic changes can be generated to make a py2.x variant. But for codebases which have to make deep changes, or make heavy use of additional python based projects, they will most likely have to branch and coordinate porting into py3k with the other python module projects.