Installing OS7 for me hung at the end with the message Importing Midi Tables. However after a power cycle it boots fine. However Rig Manager then indicated to me that I had corrupt rigs and should reboot holding the rig button. After doing this all UI has become inverted so what should be black is now white and vice versa.
Rolling back to OS6 resolves the inverted UI but then installing the beta OS7 again inverts the UI.