I'm not sure how you'd do it, and I'm sure it'd be super expensive to implement, but I'd like to see a partial or full rotating playfield. I know there would have to be shared space between the two sides of the playfield for mechs and wires and lights and such but essentially it'd be a playfield sandwich with a different playfield on either side.
If it were a partially flippable playfield, maybe only the upper half would flip. You'd do some things, reach an objective, the ball would be held at the bottom area of the playfield while the upper part rotated (flipped). On the other side would be new things to do and shoot for. If it were the whole playfield that flipped then the ball would be held below the game or behind the backboard or wherever, until the playfield could be flipped. You'd then play the other side of the playfield.
There'd definitely have to be some engineering involved to make it flippable and there'd be a host of problems to solve, but I think it would be neat. Wouldn't it be awesome if you made a shot, similar to the ring shot in LOTR and while the ball was being held, the entire playfield changed?
On a more limited basis, even if certain things could change places during the game. At one point there are drop targets on the right that then become stand up targets that then becomes a scoop. On the opposite side you'd have something similar with a couple of different things that could be in that place.
Again, anything like this would probably be expensive to make a potential nightmare in terms of maintenance, but it seems like there's so much more you could be doing to expand the game beyond its traditional elements.
Dave