Before I upgrade HA, it could announce in a voice like HAL from 2001 a Space Odyssey: Home assistant functions will not work for five minutes. You will be notified when they are back. Once the server finishes upgrading: All home assistant functions have resumed. Have a nice day.
This could be on any reboot. There should be configuration options to specify the speakers involved. The configuration should also limit the hours - don’t announce it at 2 in the morning.
This would be a lot of fun.