What component most limits a camera's frame rate?
I would think it would be image sensor and shutter speed.  The challenge of capturing enough light at those speeds is not trivial.  Whatever speed you could get the sensor to run at you could always throw more and more hardware at it to be able to process the data.  Storage mediums would be a similar story you could put as many in parallel as you wanted to get the performance you needed.

Now if you set constraints for power, size, cost etc, then that could change things.