For the record, at some point I was planning to include themes for the bottom screen in AAOv6, with the ability to select a main theme among a small selection matching all games in the series. (well, all games on the NDS at least)
Back then, my designer Meph had provided me with some mockups which looked really nice : http://gnudb.free.fr/~meph/player/index.html
(click on one of the 4 themes to select it)
I was also thinking of allowing players some simple overrides (colour scheme, background image, etc.) on the theme they selected.
For lack of time and motivation I never actually implemented it, but it's definitely doable, in particular as long as I still have Meph's mockups linked above
If any developer is interested in implementing it, they won't have to start completely from scratch !