This WORKED FOR ME!!
I had the same problem for two days. Finally, it's fixed! Basically I used Find My Phone, erased the data on on the iPad and restored it from a Backup. Pretty simple.
The iPad was stuck on this message: “Could Not Activate iPad. Your iPad could not be activated because the activation server is temporarily unavailable. Try connecting your iPad to iTunes to activate it, or try again in a couple of minutes."
I also tried connecting to iTunes. But iTunes could not recognize the iPad and suggested that I go to an Apple Store!
Details;;;;;;
After looking around the internet for a couple of days, I found a reference to turning off the "Find My Phone" feature. So, I went to iCloud.com, signed into my account and used the "Find My Phone" application. It found the iPad with no problem. I directed the application to erase the data on the iPad.
After that I connected it to iTunes and iTunes recognized the iPad this time. I restored the iPad from a backup. Unfortunately, it was not a recent Backup. The Backup from just before the upgrade to 9.3 was corrupted. For some reason that I do not understand, the most recent backup available was from Sept. 2015. But, it worked fine. I now have iOS 9.3 and just need to update some of the Apps (delete old ones and add new ones) and tweak some personal settings like Wallpaper. A small PITA but better than having an iPad Brick!