Yeah, that's what I was suggesting, the CoreRPG version the ruleset is built on, only until it's confirmed to work with the new one, in which case it's "frozen" til it's confirmed working.
This all falls to pieces if the engine api never guarantees anything to CoreRPG, because then CoreRPG versions mean almost nothing to ruleset developers, so versions should simply be "Current" or "Broken" to reflect their potential for producing a working ruleset. :)
I really, REALLY like that idea presented somewhere here that mentioned using version control, though. Imagine an embedded versioning system (at least where text files are, anyway, binary assets would be a problem) where you could roll back to any stable/compatible release, and corerpg just had different branches storing the diffs rather than a hundred billion ruleset folders? At least the images/versions that were still compatible with the engine.
Still, rulesets/mods/exts are archived themselves, so I'll bet there are headaches involved with having the unzipped versions sitting there taking precedence when an updated, zipped version is installed.
Anyway, not saying it's easy, and probably not introducing any new ideas that weren't mentioned elsewhere I guess, just making a suggestion for the mental health of everyone involved from SW on down to the guy who is like "OMG I can maybe possibly finally run/play GURPS and abstract away just the tiniest fraction of the rules so I can convince others to play"
Whether it's viable or not is left the the people who know what's going on (and who aren't too entrenched in their mastery of an existing system to fairly analyze an alternative system, but I'm assuming the overwhelming majority of people here already take that rational view)