Cool! Glad to be able to help.
I like the idea of OS update notifications, but my immediate feeling is like yours: It would probably be quite complicated to make such a system reliable, particularly across various guest OSes. There's no uniform and reliable way for us to find out that an OS update is about to take place, and, in the particular case described in this thread and many others, it would be too late to provide a notification when the OS has been updated. There are a few hacky ways we could try to guess when an OS update might occur, but all the ways I can imagine right now would be prone to either false negatives or false positives. Still, might be worth some continued pondering (when I have some available ponders).
Thanks,
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Darius