Huh?
Take Ogledow (?) for example. with the current max of 32 players and autobalancing on, we have 16 players for each side. Each side also has..what, say 6 or 7 Tanks at its disposal, each tank w/ 3 Positions, that makes 18-21 positions for the tanks alone, so there won't be any infantry left as it is right now anyway. Whats your point then?
The addition of a commanders position would not change one thing regarding the infantry issue, all it would do is give a dedicated team of players, such as a Clan, a more effective means of operating the tank.
And what inhibition to gameplay are we talking about here? If the commanders pos. is not manned everything would be the same as it is now, the gunner in its dual role of operating the gun as well as scanning for targets & trying to keep things under control (situational awareness), the driver & hull mg. WITH the commanders pos manned the gunner could concentrate his efforts on destroying enemy tanks while the commander keeps scanning and calling out targets, thus making THAT particular tank a more effective weapon etcblah...