I went ahead and tested this to see what would happen if I did click 'yes' on the upgrade prompt to Ubuntu 18.04. As the team suspected the upgrade to 18.04 failed because it was unable to get an exclusive lock, so while this is ugly it won't actually break anybody. Additionally, if I recall correctly the release upgrade prompt is on a timer so if somebody received a prompt to upgrade to the next release and clicked 'yes' they shouldn't receive a prompt to upgrade to the next next release. Attached you find a screenshot of the ugly.
And for future reference to recreate this I manually ran check-new-release-gtk a couple of times while the upgrade was in process (i.e. after the downloading phase) until it finally worked.
I went ahead and tested this to see what would happen if I did click 'yes' on the upgrade prompt to Ubuntu 18.04. As the team suspected the upgrade to 18.04 failed because it was unable to get an exclusive lock, so while this is ugly it won't actually break anybody. Additionally, if I recall correctly the release upgrade prompt is on a timer so if somebody received a prompt to upgrade to the next release and clicked 'yes' they shouldn't receive a prompt to upgrade to the next next release. Attached you find a screenshot of the ugly.
And for future reference to recreate this I manually ran check-new- release- gtk a couple of times while the upgrade was in process (i.e. after the downloading phase) until it finally worked.