Just a few thoughts,
that couch that is in there now, is not the most light-weight thing in the world.
I have a regular futon in our 3295, it does not pull out as far as what that couch did. Takes up considerable less floor room when in the "bed" formation than did the couch.
I believe there are a few MOCers that have changed from table to dinette/booth.
Chairs that come with these units also are not light-weight, so pulling them out and replacing with a dinette/booth may not be any big weight difference.
As far as the bunk bed thing, get out the ruler!
Interesting suggestion, let us know if it will fit.