I have done it. I got a single folding leg and a wall hinge at a local RV supply store. The leg folds up tight to the bottom of the table when used as a bed. The wall hinge allows the table to drop to the bed position while remaining attached to the wall.
The challenge is finding a secure way to mount it to the wall. Most of the walls are hollow, and a stud in the right place would be real lucky. So I suggest mounting a large piece of wood, like 3/4" plywood to the wall. With that it will be able to be attached to the wall wherever a stud is, and then the hinge to it. It can be stained etc. to match pretty good.
With a solid wall attachement, the table will be much more solid than it was before the mod.
