Converting Unmanaged to Managed devices in iOS 7 OTA
If all you care about is enrollment - you should be fine. OTA supervision isn't yet being provided according to all the information I've seen as of late October 2013.

There is great confusion out there as Apple did promote the idea that OTA Supervision was coming with iOS 7. That feature was dropped from the public list of features about a week before release and there is no official word if or when it may come back.

There is a difference between iOS supervision and iOS MDM enrollment. The latter item is easy - most all MDM can enroll devices over the air on iOS 6 and that ability continues on iOS 7.

Over the air supervision is not possible on iOS 6 and requires Apple Configurator to supervise devices before you choose to enroll them into MDM.

Over the air supervision is not possible on iOS 7.0.2 and even the 
"streamlined MDM enrollment" that is still listed is either not working or waiting on the MDM providers to update their software to take advantage of those new settings.

I would expect by late November, there would be good indications that we will or will not get OTA Supervision with iOS 7 this fall as well as which MDM providers (if any) work with the "streamlined" enrollment methods.



And a footnote, there are several reports that a bug in iOS 7 upgrade has caused a portion (but even a portion of 7,000 iPads could run into a hundred devices) where supervised iOS 6 devices were removed from supervision as part of the upgrade process to iOS 7. Anyone affected should contact AppleCare for assistance if you don't want to simple re-supervise the devices.