My idea would be to have certain dead zones on larger maps rotate so that parts of the map become accessible or inaccessible on a timer. For instance if we take Zikurat:

Each of the coloured zones could be enabled/disabled on a rotation, say Blue+Red Disabled, then after 1 minute Blue+Red enable, and Green+Orange disable.

Such a configuration could be permanent (so a game can be set up with Blue+Orange permanently disabled and act like existing game modes) or dynamic, which would function as a new game mode. The flags are only capturable when those zones are enabled. This places a large focus on capturing flags within the time they are enabled, so the flag bonus is still provided when the flag area is disabled.

I think this would tackle the problem of low amounts of existing map assets (which are pretty expensive) to be used for lower player numbers. 

I personally enjoy games with 2/3 players per team more (maybe I just need more friends) but this basically leaves us with only 3 maps. I think this gamemode would serve to give alot more choice with relatively little work to Demigod as well, and add a few more bullet points to the games portfolio.

EDIT: Also, for the purposes of what happens to a demigod when they are in a zone when it is disabled, obviously the flag should be locked, however and increasing health degredation the longer they are in the zone could also be used, perhaps even without flag locking. So if a demigod feels it is necessary, they could remain in a disabled zone with pretty heavy health loss in order to finish off a capture. 

Infact, simply just basing the entire gamemode around health loss areas really reduces the amount of coding involved (at least in my head) and the possibility for exploiting and having to design code around blocking players access to disabled areas. If a demigod in a disabled area just gets health degen, then they can enter and leave it freely, and then learn the hard way. Perhaps the areas could be shrouded with a red mist, using already existing assets in terms of the fog of war.