customizable 'design your own' flexi-troop
this is a bit out there, but would enable creativity....
how about the highest level barracks troop offering would enable you to design a one off customisable troop where you set the parameters (which an algorithm controls so that different features offset each other to give it limits and stop it becoming too OP, and prices it accordingly...e.g. faster speed means less damage per second, to target air and ground units costs extra etc), and can choose from a range of colours, designs, shapes, and give it its own name?
as you can probably tell, i haven't thought this through a great deal yet, but i thought it would be good to put it out there and see if you thought it had potential!