I get that standardizing the versioning would remove a lot of headaches for experienced modders. It is really annoying when you spend the time posting details and a user disregards them, slaps a million mods on, and gets mad and flame posts that your mod doesn't work, the game is buggy, etc. I think we can all relate to that being frustrating when you have spent so much time on your work.
I'm going to have to echo what many said here, though, and say I don't think strict version management like this is good for the community as a whole. Standardizing the versioning is fine and I think the guide is very helpful, but having additional software purposefully lock out a game load or cause a well-meaning CTD creates a larger barrier of entry to would-be modders and even more unrealistic expectations of end users.
Why? A new modder has to have intimate knowledge of what causes saves to break. That is definitely a learn-as-you-go kind of thing and as the code base of a project expands, more things can go wrong in that regard. So they have two choices:
A) Release every version of their mod as a Major release so they protect themselves from additional flak from end users - since there would then be "no excuse" for a save-breaking update as a Minor or Patch update from the perspective of the end user.
B) Release the actual version of their mod considering the added content/etc, and risk being wrong and the save being broken. In that case, again, end users now have higher expectations and therefore greater wrath than before for mistakes. That point also goes (possibly doubly so) for experienced modders who make a mistake - which will likely happen from time to time.
Option B's downsides are self evident. Option A's downsides are a lack of clarity on actual content contained in a Major update. What this would likely translate to would be: experienced modders generally follow the guidelines (except then they don't! - because they know a hotfix breaks a save, etc) and release a lot of additional content under the Major update. New modders will be all over the place, and the frustration of the end user when a problem occurs will be greater - not less - for situations where a save is broken because they had a false illusion of safety. Those situations may happen less as a whole, true, but it is skewed in the benefit of those with experience - as would be the Major update in general since more experienced modders can take better advantage of it and bring more consistent results (that end users now expect!) each release.
So, imo, even though the desire for SemVer enforcement is well-meaning, it doesn't *really* solve the problem at the end of the day. It ends up making things more confusing for everyone, end user included, and makes a new modder's job even harder.
SemVer is great for tech companies and technical teams to manage their version control and choose release candidates for low-margin-of-error production environments, but it really has no business being enforced in a hobbyist modding scene. When a mod update breaks saves, it may annoy some end users, but its not like you are going to have to explain to a project manager why the release went so bad. It's a hobby you are doing for free.
Now, all of that being said, something like what was proposed
here that would allow a modder, themself, to create CTDs based upon versioning within
their own mod - and not globally to all mods - would be ok. That way, a modder can opt in to the additional pressure of increasing user expectations by controlling their mod's launch-ability when encountering mismatching versions. Unfortunately, that will still create situations where an end user posts on a newbie modder's thread wondering why their mod doesn't police its versioning like X mod does, but that is at least better than a universal standard of expectation for releases as would be found in a professional environment.