This isn't the first time it's been proposed. We could also consider hypothetical Gravastars.
The idea of Gravastars somewhat complicates the concept of a universe within a universe. Gravistars are thought to contain maximized condensed empty space. You can't get it any smaller. So, how would we survive inside a black hole, a place with significant crunch going on? But I guess density could be relative. You could crunch more, just not so easily, in our own universe.
Concepts beyond me, but always fascinating.