I'd say, the sky is the limit, but would highly suggest to keep it real, keep it practical. I shoot quite a bit of steel matches i.e. PRS, NRL, C&D, and it appears there's this trend to create ridiculous stages. When I say ridiculous, I mean non-practical. It has really gotten out of hand in my opinion. An example is place your rifle in, and supported by a hangman's noose, or shoot inside a tube supported by springs. Just this last weekend, we had a match on a ranch that has an unlimited amount of natural terrain, but the Match Director decided to add a stage where you shot sitting on a saddle mounted on an elevated 55-gal drum, and another stage shooting off a suspended chain. I understand that a square range can only offer so much in the way of positional options, but you need to keep it real. When I say real, don't create a stage that you would never shoot a rifle in that position in real life. Another example... Many people Varmint or Preditor hunt shooting from a truck window, hood, or bed. So make a stage that incorporates a vehicle. But don't create a silly stage shooting of a wobbly swing set.
Another thing, don't limit how someone wants to shoot at the target (position or gear), let them make the choice. Some matches force you to shoot prone, non-supported, and specify you have to have your elbow resting on the ground or on a rock, and you cannot have an elbow pad or padded jacket. I have nerve damage in my elbows, and that kind of stupidity just causes problems for people like me.