So, most FOC swaps bring an elite or something into troops, and I think when that happens they should be just like every other troop choice -- as long as you have one of everything, you can bring as much as you want. Farsight armies have to have a kroot and a FW squad, but can then take as many Crisis teams as they want. Draigo wing would have to take at least one unit of Strikes before they could take multiple paladins, etc. (if they took coteaz, too, most do, they would also have to take a henchmen squad, but that doesn't seem like a problem)
In the case of the same unit that can be taken in different slots -- Daemon Princes, tervigons, some dreadnoughts, etc, I think if they're in a different slot they should count as a different unit type. So, daemons could take a DP in both heavy and HQ, if they took the right kind of greater daemon, for instance.
BTW, my standard list has both a reg Tau crisis team, and a farsight troops crisis team -- I would think those count as separate units. A better question -- does my commander from Tau and the commander from farsight both break this rule? Or is it ok cuz they're allied in?
I think dedicated transports should get a 0-2 exception. I think wholly mechanized lists sorta fit the "spam" idea that this rule is trying to prevent (it's trying to overwhelm you in a specific area....it's the opposite of balanced), but at the same time, yeah, some armies only have one transport and it doesn't seem cool to say they can only have one transported unit. SM and the like can get 2 razorbacks and 2 rhinos, but that's not going to break anybody.
Actually, thinking about GK could get 6 transports, and that doesn't seem right. Maybe 0-2 as long you only have one dedicated transport available?
Yes, squadrons should be one choice, after all they only use up one slot. Just about anything that only uses one slot should count for only one.