Jcoats...what a wonderful idea! I have mentioned in previous posts about wanting to build a panel-saw style router, but could never get around the issue of fighting gravity when the parts are cut out (however I did manage to work out the issue of holding the sheet down using angle iron for registers at the lowest end to the floor and at a perpendicular angle running vertically...this allows one end to load, unload...with a fold-down angle iron "vise" mounted at the top using piano hinge...I digress).
Two issues that pop up in my mind...the issue of the Z carriage height...and ensuring the table is level when folded down for use.
Aside from cutting a hole in the wall and building a box out the side of the building structure, I'm thinking a fold-down gantry would allow this concept to work. Not sure how stiff this would work out in a real-life scenario, but I'm imagining "wings" that fold out and clamp down to the X axis carriage.
As for ensuring the table is level, this could be fixed easily enough by having a register on the floor that the fold down legs would anchor into, to assure a consistent (relative term) measure of levelness. Of course you'll want as little play as possible in your Murphy Bed router-table pivot that allows you to rotate it up into a stored position.
I'm definitely going to be following this build!