One of the things that bug me about pinball these days is the sameness of the designs. The cabs are almost always the same dimensions, sometimes widebodies. We tend to see the same layouts again and again with little variation. A single lower pop bumper is a huge anomaly and cause for commotion.
One idea to mix it up would be to vary the balls - an iteration of the Powerball concept. This could be in the form of:
1) Smaller ball (1/2 or 3/4 scale) to allow for more and tighter shots and unique playfield designs. Sort of the opposite of Hercules.
2) Mix up standard, power, and mini balls in multiballs or in different modes