[atoav]

I do understand that, my point was precisely that this is always a tradeoff between multiple things. If maintaining the old version is easier than migrating to the new one, you don't do it.

This balance — however — can change with time. E.g. if one of your major dependency moves to Python 3? Or gets abandoned.

I didn't say it was easy, my point was that over time more and more dependencies make a shift to Python 3 as well, which means at some point Python 2 stuff becomes harder to maintain. Whether that point happens early or late depends entirely on the project.

Additionally I nowhere said that this must be done by anyone — you are projecting here.