A couple weeks after bringing it into the house, it started to warp (concave up), as the maple/cherry dried. (D'oh! I don't usually have this problem, due to the damp winters here).
Anyway, I'd like to fix the warp. I'm thinking I'll take a router to the back side and eat away all the plywood inside of the edging, down to the hardwood. I'll cut another piece of plywood to size, and after allowing the backing and surface to acclimate inside for awhile, glue them back up.
Any problems with this approach?