This really changes the game BIG TIME for box speakers now !..
Not really. The KEF is still a box speaker. 
Absorbing most of the backwave as advertised sounds really good, but would like to see some tests to confirm the effectiveness

I dont know where you read that it absorbs most of the backwave. It does not. The absorber is only used on the tweeter. Not the woofer. 
kenjit

Steve Guttenberg said these Meta’s sound like Open Baffle speakers and that’s a real.. game-changer for Box Speakers...

The best of both worlds !

https://www.youtube.com/watch?v=oKTYvP7YQ0Q&t
 
 I can't wait to hear the Kef R11's with this new Technology !
I have the KEF LS50's, and I am very pleased with them.  I am considering upgrading to the Meta.  What should I do with my old LS50?  Can I use them as surround speakers?  They seem to need a lot of power.  Where would I sell  them?