Thinking about doing 2000 kicks made me tired!
I think there may be a point where the exercise becomes non productive. You can practice kicking a target, bag or shield for many reps or minutes or rounds or whatever and it can be productive. It can work on that mental edge to go beyond pain or fatigue, it can be anaerobic or a number of other things productive as long as it stays within the bounds of
reason. Once you get to a point where you are only waiting to get to the end, I think it becomes a waste of time and non productive; especially done in air. You can do 50 or even 100 worthwhile kicks or you can do 1000 that accomplish nothing. There is a difference between doing something a lot and doing something good.
In my opinion people that practice 1000 (or 2000) kicks only become good at doing 1000 kicks. (or any other technique).
I always liked the quote someone quoted above.
"It's not the fighter who practices 1000 techniques you have to worry about; it's the guy who practices one technique 1000 times."
That doesn't imply 1000 at one shot. It only means he practices one thing completely rather than a multitude of things half assed.