RE: Dual Servo?
Many years ago Kraft (I think) made a "brick" that had the RX and a couple of servos all in one big box.
I've never seen anything like what you're talking about though.
I have seen guys widen or otherwise modify the opening in the center of the wing, use servo tape to stick two servos togther, and mount two smaller servos together where one larger servo should be to drive torque rod style aileron linkages so they could set up flaperons. It's easy enough to do. You do need to trim some arms off of the servos so they don't interfere with each other.