I think there can be
some limited use of looping in prog rock, in as much as anything repeats itself, occasionally. But indeed, the very essence of what is progressive is that the music changes, and evolves seamlessly throughout the song [chord progressions and key changes].
I was just reading the latest KVR interview, featuring Trevor Rabin, and then subsequently listening to songs from the Union Tour. Prog rock was at in it's finest hour, then, and I'm glad I got to see some of the bands that are no longer playing.
I can't blame people for wanting to try to recreate some of the magic of progressive music. Nevertheless, I wasn't enthusiastically impressed with these particular loop offerings because they lacked some depth of sound quality- at least to my ears. Still, they might be desirable for some people.