This is not a new concept, but would be interesting to have it implemented in AH.
A neutral base does not belong to any country, and its acks will shot at any plane or vehicle in range. These bases dont rebuild their destroyed structures. When the acks, hangars and barracs of a no neutral base are destroyed, the base is abandoned (no defenders) and becomes neutral (shown gray on the map). After a reset, each country receives 6 airbases, 2 near the HQ and 4 adjacent to other enemy bases, and some vehicle bases. The rest of the bases on the map are initially neutral.
Imagine a PAC arena map like this, being 'N' territory with only neutral bases and 'O' Ocean at startup:
OOORRROOOO
OOOOROOOOO
OOOOOOOOOO
NOOOOOONOO
NNOOOONOOO
OOOOOOOOOB
OOOOOOOOBB
KOOOONOOOB
KKOONOOOOO
KOOOOOOOOO