The MLS has tried some changes to aid that - if you go off you have to stay off for a minute I think, and if you hold up for a sub, if the players doesn't get off in <10 seconds, the playing coming on can't go on until the next stoppage (but the player going off has to go off).
Don't we have a 30s rule in football for coming back on now.
They did try and speed it up with subs going off the nearest touchline, and with multiball. Obviously for subs you get the fake limp or, my favourite, the jog that's slower than a walk.
I like the 10 second rule though
