Alternatives...
On my E-25 I've wondered whether it'd be advantageous to build such a structure... by making some cross-pieces and some plywood, this would make the use of an inflatable queen-size mattress almost painless...
And, yeah, the timbers across the cabin would have to be notched in such a way that they'd not weakened... (imagines how weird these can look)
With a little bit of cleverness, I can imagine how this'd be notched for the mast compression post and how the "plywood" pieces might be able to fold over into a table (of sorts). The problem, of course, is where the flat *and* cross pieces that are superflous in building a table could be kept w/ no impact to "productive use of space".
The key being that you'd use an inflatable mattress for weight and "lowest inactive volume" but then the *rest* of the structure would suck up a fair amount of volume when not in use, though a LOT depends upon how heavy the crew is.
Note that _my_ E-25 has a full keel and so this, I think, simplifies matters, at least for *me*.
Hmmmmm...
In any case, as hcpookie commented, the key trade-off question is how much space is lost when this is NOT in use... and what kinds of tricks can be used to mitigate the lost space. (Hmmmm... a roll of bamboo?)