The depth of the pit is actually more related to the height the arena is off the floor. Since you have to raise the whole arena off the ground to get a decent depth of pit then it gets a)very heavy b)very expensive and C)more complicated to assemble.

It is currently up for debate in either direction but it will fall to the EO's and the FRA to decide what the rules are at any given event.

At the champs at GSL for example, I believe the rule is that touching the bottom of the pit counts as out, this stops flippers from being able to escape and machines with large wheels have to be weary of it like every other team.

Personally I agree with that ruling, it gives EVERY robot a chance to win outright of their weapon fails or if they have no weapon (though I am not a fan of bricks or boxs after your first event). The same logic could be said for an OOTA as some flippers are so powerful they could in theory fire themselves back in they were lucky.