I did eaxactly the same flashing operation as before with Android 4.4. It took some time before Android 5 booted. I guess Nexus 7 (2012) is not the fastest tablet around anymore.
When Google makes Nexus factory images available I will flash my Nexus once again. Just to make sure all is well. Meanwhile the leaked version of Android 5 is the best there is.
My Nexus 7 wifi (2012) is sooo happy now!
Info is telling there is Android 5 inside!