This is more of a curiosity that anything, I suppose.
I've owned three pins so far, a Twilight Zone, Addams Family and Tron LE. All three had completely different playfield mounting systems.
TAF - the oldest - has no rails at all, the playfield just pivots on two hinge bolts. This means it is nigh on impossible to get access to the back of the playfield to do any work on it. In terms of working on other things under the playfield I've found you end up having to lean over the machine uncomfortably, or reach up to get to things. Any substantial work requires you to pull the playfield off the bolts (no mean feat) and rest it on cushions etc.
TZ came out next, and had a massively improved rails system. You pull the playfield out, it locks into position and you can then raise it up. Plenty of access to things at the back. On both TAF and TZ, however, you still have the issue where if you wanted to work on something underneath you either have to kneel down and "work upwards", or raise the playfield up completely and then you're in the same position where you're leaning over the cabinet uncomfortably, etc.
Tron, being ~15 years newer you'd expect would have a significantly improved system again, but alas not. For reasons I'll never understand Stern decided the best system they could implement was one where the playfield just sits on two metal runners on either side, like a shelf. The day after I bought my Tron I pulled the playfield out to check something, felt some tension like you get on TZ just before it locks into place, pulled a bit harder and the whole playfield came off the rails and dropped into the cabinet. By some miracle I didn't break anything, but it was a sobering lesson. It never occured to me that it would be so easy to pull a playfield completely off its mounting points, that a design would allow it.
There is also inexplicably a bump on these channels which means that if you pull the playfield out past a certain point it crashes over the ridge, and has to be jolted back over it when you want to put the playfield down (I used to lift it from the back, and from what I've heard of JP now there is a handle at the back to do exactly this?)
Don't get me started on playfield props either... What on Earth purpose do they serve other than to demonstrate how a playfield will flex and twist under its own weight? Are they supposed to make it easier to work under the machine when they don't hold really hold it up at an angle that makes working under it any easier? I used the one on TZ once, saw the playfield twisting and vowed never to use it again.
So why has there been no innovation in this area? Gas assisted lift? Being able to have the playfield come completely out of the cabinet on all sides? Is there just no real demand for this innovation? A case of you don't know what you're missing until you see what could be possible?
Curious to hear thoughts.