This was actually a feature in RTB v2's add-on uploading system but I removed it since I didn't see much value in it and nobody really used it. The most I'd be willing to implement would be a "minor update" checkbox which would just increment the version number by .1 but I can't really see the benefit in having huge granularity for version numbers.
Add-ons are usually pretty minor on their own, compared to the game as a whole. RTB makes use of it pretty well, separating major content updates from bugfixes, but I doubt that would mean as much when used to identify an update to a shotgun, which doesn't have much room for major content updates. On top of that, you'd have to worry about the variety of opinions on what constitutes a minor update. Some people may never even use it so you get inconsistent version numbering between add-on developers.
However, as I mentioned, larger add-ons like RTB make use of it well, so there is some room for it. Perhaps large scale moods like Team Deathmatch, CityRPG mods, large content packs, and other minigames, could have a use for it if they are the kind of thing that may have either kind of update.
I say only put that feature in if it comes with a way to determine which add-ons would have need for that distinction, and then only apply it to those ones.
