Clever stuff. Of course for 2 dies you could do face to face bonding.
That should give phenomenal contact density, but only for every 2 die pair in the package.
I guess they're seen the layers between the dies as sort of stress relief layers to absorb some of the forces involved, deforming to accommodate any forces in the dies.
Intriguing to see if they will go to some kind of processing-in-memory that has been proposed off and on since the mid 80's.