Many a time I have become an engineer or rifleman, and an enemy tank suddenly shows up at my base. I quickly commit suicide and switch to grenadier to take it out. I think it would be a great if one could switch class at the armory, similar to Battlefront 2. The armory currently just acts as a ammo and health bunker, but it has much more potential. Also, this would be more realistic, as one in "real" combat could put down their rifle and pick up a rocket launcher.
Er... You can switch classes in the Armory. Just bring up the class selection screen, switch to whatever class you want and click Accept. You can do the same in the Barracks and near captured flags.
what? you can kill yourself? Crap been doing it the hard way the whole time by running back to a barax then changing.
You don't have to reload your weapons if you suicide. =D Sure, you wait 3 seconds to respawn, but you reload both your mortar and RPG (which is 3 seconds each) and you don't risk getting killed while you're reloading (because you're already dead). It's the perfect strategy!