I dont want to make this post Neonstorm like with too much text and formulas so keeping things rather simple.
Other RTS'es have it to prevent lag and needless spam so why avoid it here? Specially when zk have such cheap spammable units like fleas, dirtbags and darts. There would be great advantages:
*Easier to define minimum system requirements
*No spaming crap to kill all weak CPU players in dirty way.
*More consistent framerate during whole game.
Now obviously this unit limit couldnt be static per player. Very basic formula should be global unit limit calculated from map size and divided amongst all players. This would mean small map = many units big map less units, more players less units per player etc.
Unit limit could be visible on economy bar with max allowed and current unit counts.
PS. I personally now have 4670K and actually playing on max settings without lags, but I still remember old times and I feel for players who lag.