Handled properly, concavity of plane soles won't be an issue on material longer/ wider than the plane. The edges being true with each other assures the relative flatness. With the throat matching perimeter, setting blade depth remains same as the very best made plane would be. It's a toss-up about friction reduction, lesser contact is certain, but might be air cushion instead of reduced surface.
Some heavy fixtures introduce compressed (filtered) air for movement across surface plates, no recess, just vent holes connected by slots, need be.