I think the CNC device mounted to a wall will work well. You may have some setup issues with getting the rails straight and in line. Most walls vary in and out.
I would add something to the table for positioning and locking to the wall. That way if you move the table out of the way, you can get it back in the same spot.
If your table isn't heavy enough, your router might move the part and the table since they are seperate. Locking this in will solve that issue.
It will be vital to use the machine to skim cut the top of the table for squareness.
If you are cutting parts all the way around, you should be OK. But if you want to position a precut blank against stops and only do some interior machining, you may have registration problems. Again this is caused by the table not being fastened to the CNC.
I'd say go for it!!!