While performing the upgrade from v6 to v7, I've found that trying to go through an add a new license key after the App_Offline.htm file was removed still has the site down for a certain period of time, with no custom messages besides the default "No license key found for this domain"

It would be nice if there was a maintenance mode for the system, that would allow you to either put in a message or redirect to the a different link like offline mode does, but is general for the site, so it wouldn't matter if all sites are put off-line. When, like my situation, you have 14 websites to go through and declare a file for redirect and put each site offl-line one at a time, it takes quite a while.

As stated earlier, having a Maintenance Mode would be general for the entire application, much like how off-line mode works for each site. When upgrading license keys, it shouldn't affect maintenance mode, thus allowing the admin access to the CMSDesk and CMSSiteManager for adjusting settings, license keys, sychronization, etc, until the maintenance is complete.