EOL dates of prominent Linux distribution :
I think I would need more information than that. Nick's proposal was more specific: when does the vendor stop producing patches? This is a clear criterion, and one that I support.
My interpretation: Python support until end of production phase 3 (7 years).
I'd prefer something more official than Wikipedia, though.
My interpretation: Python support until end of Extended support phase (7 years).
So by this policy, RHEL and SuSE users would be off worse than with my original proposal (10 years).
Considering the nature of the Fedora project, dropping unsupported fedora distributions may or may not be helpful for Pyhton and it's users.
Again, for Linux, I think the issue is somewhat less critical: in terms of portability and ABI stability, it seems like they manage best (i.e. we have least version-dependent code for Linux in Python, probably because a "Linux version" doesn't exist in the first place, so distributions must provide source and binary compatibility even across vendors, making such support across versions more easy).
Also, it is not clear what to do about distributions/OSs without any official EOL or life cycles.
Here my proposal stands: 10 years, by default.