i've though of this for the ww2 games like return to castle wolfenstein. but that game has some advantages with defending and attacking teams, objectives and different team roles. using a map over an area and a campaing that lasts like a week or so, or a day. later i found out there was already something like this:
http://www.battlegroundeurope.com/scripts/wwiionline/index.jsp but i felt that battleground europe had no action and was too slow, it was also very difficult to begin with. and it costs every month.
but i'm not sure that openarena would be the best environment to build upon.