@Rycaut fortunately that next step about the mechanics of alerting users is comprehensively solved and very well tested already, and the business has very conclusively decided that multiple user databases will not be an eventuality this team will need to care about.
(That's where most of the heavy lifting went over the last couple of years, which is why I now have the luxury of puzzling over a nicer, cleaner way of doing this one small thing instead of using our existing hack-job tooling.)