Well, I had a spare morning, and threw together a PoC: https://henthighschool.net/hhs-mods/mod-1-10-4-2-proof-of-concept-violet-beauregarde/

Note that I didn't actually implement many events, but the framework's there. It's a bit too fraglie for my taste, there's a few event-design issues and a few engine issues that prevent it being nice, but in theory most quest-chain events could be added with only a small amount of effort; I suspect there's a lot of corner cases to watch out for though.