You've mentioned it already, but the first thing that popped into my mind when I read this was QGIS. The problem here is that version numbers mean different things depending on the software. You can't really say Arc 9.x, and depending on what you're asking about you can't say 10.x either. I don't know enough about how QGIS works - if it's similar or if you could do 1.x, 2.x etc. (my guess is not).
Because I am also not familiar with Python to that extent, I cannot offer an informed opinion whether coarser or more fine grained version tags should be used for Python. If an obvious, logical numbering break isn't used by the software (ie, 2.x and 3.x) to determine what a "significant enough difference" is to warrant a tag, then who or what does? (My point here being this proposal seems like a reversal of your earlier approach logic - what if I only have and can test 2.7, not 2.6?)
A post on another meta raised the issue that I did in the earlier question you linked to - if the question isn't version function specific, it should only have the generic language tag. Otherwise the version tag becomes meaningless unless you are already familiar with what changed when.
As blah238 points out in his answer to that other question (and provides several relevant links), different SEs have different approaches to version tags. SuperUser said two Firefox tags are plenty. StackOverflow had a resounding no to that idea. I don't want to regress this too far back to a version tag debate - that's what my question was for, and this one is specifically about Python, though it's obviously rooted in the larger question.
I do agree with the formatting consistency improvements (hyphens and dots). But as mentioned above, I can't speak to which versions justify their own tag vs being part of a parent version as a synonym. I also don't think python general and python version tags on the same question is a good way to go. I'm already sick of seeing arcgis version only (because I don't follow every single version, just desktop), and it still feels very redundant to have both desktop and version tags on a question (though I understand the logic and don't necessarily disagree with it).
Related question: Is there a default assumption as to a version of Python? which also links to the Python tag Wiki on SO, which basically states no version tag preferable, version family tag if needed (#.x) or version tag if it's really that specific. Note that the Wiki does advocate use of both general and version tag on the same question, which differs from my opinion in the previous paragraph. However the difference is the version is only applied to cases when needed and not to every question where asker is using that version. In theory/my opinion this produces much less tag redundancy and increases the value/specificity/usefulness of the version tag.