That 100A breaker will trip if the current exceeds 100A in either of the poles. So, f you wire both ends to the same service conductor then you can have a max of 100A in each pole of the breaker and 200A combined in the single service conductor. So, you got it right earlier.
I think it could exist. One of the things that has been claimed for smart meters is the ability to shed loads, though how this would be done I have never seen explained. This is one clever way. If the meter also were set to cut off power all together if the load exceeded a certain level, eg 100A, then it could solve the potential overload problem when the 240V load shedding is used.