Have any pinball machines ever been designed to change the difficulty during game play. Some sort of algo to make the bumpers less bumpery, restrict the movement of the flippers, adjust the angles of things, etc?
Not to my knowledge. It would be antithetical to the game. Games do scale difficulty based on progress but this is the same for everyone. Some games do reverse flipper sides or direction but again, it is based on progress, not a more complex playtime targeting algorithm.
An example of this is multiballs. The first one (per player) can start with say three shots. The next one might require six and then the third nine. This is oversimplified but the point is the progress is consistent.
The only dynamically-scaling feature I am aware of is the replay score which (can) set a starting score based on recent plays but will also scale up rapidly when it is reached (say, +50%) until it isn’t reached, at which point it resets to the starting score. But this has no actual in-game effect.
