What is the expected behavior when iPads already enrolled with DEP and supervised in IOS7 upgrade over the air to IOS8. We have already instructed our students to wait until we give them the go ahead but some will do it anyway. Last year we had an issue with some students going from 6 to 7 losing supervision.
I would expect they resolved (and tested) the supervision upgrade after the fiasco last year. I haven't tested this workflow, but iOS 8 with DEP/Supervision works as expected.
You may still want to block Apple's update server (https://mesu.apple.com) for a few days. If they take them home, the will still be able to update but it will help keep normal school traffic from coming to a halt for the iOS update. Also, if you haven't looked at Caching Server in Mavericks Server, do this quick. It will save you a ton of bandwidth!
Having just done this on my work Casper managed iPad Air. I have comments, but only for Casper 9.4:
While a fresh iOS 8 enrolment does not appear to work (I need to do more testing, so far only tested personal device enrolment), an iOS upgrade does work.
The Casper 9.4 Self Service app would appear to need re-installing, this should be performed by having the user delete the app, then from Casper push out an inventory update to trigger Casper into pushing out the Self Service app again, with it's settings.
I performed the upgrade via iTunes (since not officially available until next week) with backup, restore from file, restore backup, but I assume it will be just a smooth.
Our experience has been fairly similar to @wakco. We have upgrade several DEP, over-the-air supervised, iPad Airs using the device restore functionality in iTunes. After upgrading to iOS 8 GM, the devices are still enrolled and supervised as expected. We did have to re-install the Self Service app as @wakco mentioned. We were also able to restore a backup from iCloud successful.
From our testing, it looks like we'll be in good shape for the release.