All of your appliances would have to remain in the fixed portion.
Sliding frames aren't new.
48’-80’ EXTENDABLE FLATBED TRAILER
The sliding portion you could add some wall mounted fold down beds similar to.
New folding "workbench" - Pirate4x4.Com : 4x4 and Off-Road Forum
Recess in some LED puck lights above the beds (or if bunks, put some into the bottom of the top one).
Or if you don't want to fuss with the hinge portion, you could use permanant hooks on the wall and then create some storage for the flat boards and removable support legs.
I'm full of ideas, a few of them may even be useful.
And none of this means you can or should create a stretch AS..