You can do a decent amount of customization in WoT, and it's not like the game is that complex. Still, do you want to see more customization options available?
I personally would like to enjoy user made custom tanks in World of Tanks. That is; for example the ability to adjust armour vs speed (Increase armour at the expense of speed and vice versa), Increase fire power at the expense of loading time and such. Another feature that I would like to see in World of Tanks is nation free tanks, tanks that don’t belong to any nation. Because that would help in making the choice rational rather than emotional (For example one might like the E100 Heavy tank but wouldn’t want to drive it just because it has Nazis emblem on it).