I had the same idea a few month ago, but don't posted it. It is another thing on the feature vote list, which will never be implemented...
If u are on a speed server and u kill 30 players in 10 seconds, u would hear 15 sounds at the same time. That makes no sense.
I don't think, that the original sounds are free, so we need some other sounds. They can't be as good as the original ones.