Chatting with @colemanw earlier today, he pointed out that some of the core extensions haven't had a version-increment in a long-time -- even though they are actively developing. We both felt that these versions should auto-increment in tandem with the core version.
One after-thought... some of these exts are flagged as beta stage, and I think that's an important signal to preserve (for admins who are browsing the "Manage Extensions"). I guess we just append the alpha/beta signifier, though it may have some funny edge-cases.
If the ext's develStage is stable, then track the core version exactly (5.39.1, 5.39.2, 5.39.beta1). That's easy enough.
If the ext's develStage is alpha/beta, then I guess we'd append that (respectively: 5.39.1.alpha, 5.39.2.alpha, 5.39.beta1.alpha). That last bit's weird, but I can't see how it'd break anything...
I personally don't see the need to do anything fancy with the version numbers. For better or worse the info.xml has this <develStage> tag which signifies alpha, beta or stable so that's the place to look for that information - it doesn't need to also be part of the version number.
Well, I think a lot of extensions do their <version> with an alpha/beta signifier because <develStage> isn't particularly visible. Note that there is no "Devel Stage" column (and, if there were, it would be redundant half the time). Also, note that a reasonable viewer will tend to infer: "if these two rows have a version# that mentions alpha/beta, then everything else (which doesn't say alpha/beta) must be stable."
I guess we can find another way indicate the devel-stage...