Honestly, I'm against it. I haaaaate class limits, even on my own team when we have 7 dickbags playing the same one class. Why? Because generally speaking, when you have people spamming one class, either the map absurdly favors that class, or they're idiots.
If it's the map, then we need people playing that class, we need to see exactly how it's being abused, where it's being abused, so we can look at how to counter. If it's just people being idiots, they're going to be idiots anyways. Either warn then kick, if they're really just mucking it up/trolling, or it's not gonna help if they go any other class. A bad player by any other class will still be a bad player. I never understood the misconception that a retarded player playing sniper will suddenly become a valuable team player if he's forced to play another class.
Additionally, if they're idiots, then maybe we DO need one good player in that class, if the server is limited, you're essentially locked out of that one class. Imagine you limit medics to 3, and 3 stillbirths decide to go "BATTLE MEDIC, NO HEALING LULZ!". Suddenly, an a/d map of any kind becomes impossible to win against a decent team because nobody can switch to medic to uber, and those 3 abortions certainly won't.
I mentioned medic but this can happen with any class. I've had it happen to me during the sniper/spy update when our team needed one good sniper to take out the enemy's defenses... and all 3 snipers were either using the huntsman (and therefore completely useless at everything in every sense of the word) or just about as good a shot as Michael J. Fox would be during one of his crisis...
At the end of the day, I think class limits just do more harm than good, and I haven't seen enough "class spam" issues on our servers to warrant it IMO.