When people say that leaning to the slits should phaps be an option once you are inside (2 positions), then more and more I think this should be done with a further roll of the mousewheel down (just like the driver does), and the gunner should be a complete new position in the tank. You could go to gun with a key press instead, or, as we are on the brink of 64 player servers anyway, a four man tank crew.
But to keep people happy, maybe the tank still reloads in the absence of gunner as long as someone is present in commander position.
It doesn't matter, because i unfortunately doubt any of this will be implemented, but i love both your ideas- and the option of 4 man tank crews as well.