I was actually thinking along those lines as well. It indeed is not fool-proof but what are the odds they’re releasing a new version within 24 hours? Then you can also set the delay to 30 days and it won’t matter.
Though there may be an extra snag, as I was looking at the announcements section and it looks like sometimes things are duplicated in multiple release notes, sometimes they’re not. Also what about Public vs Beta channel? People on the Public channel will only see release notes for versions released there, and if you don’t have a Plex Pass you can’t even check the Plex Pass versions. So there are more caveats here … don’t forget about what you said yourself before about the notifications and perhaps it applies for this too: Priorities! 
I have a custom scanner and agent installed in my Plex but would like to keep those up-to-date as well. To update them I have written a small script to do the job, but that also meant duplicating the code to figure out the Plex location and after updating restart Plex. But if syno.plexupdate.sh has an option “–post-update-script” that calls the script provided with the option with the Plex folder location as its argument, then that would be killing two birds with one stone. Any output of the script could then be included in the notification as well.
