Well cause if it is not defended then the counter attackers will have an easy recapture, I don't think the original attackers will like that very much, hence creating some "OFFENSE, attack" and "DEFENSE, defend" for both sides in the fight for the same base!
Actually, this idea of keeping a recently captured base "in play" longer sounds like a potentially strong improvement to game play.
The simplest way to do this, in my opinion, is not have the ack reset as soon as a base is captured. I've always thought this is a ridiculously gamey aspect of AH, where all the ack instantly comes up and starts shooting at the defenders. Maybe even have all ack destroyed upon capture for 5 or 10 minutes. Or at least leave whatever ack is destroyed down for at least 10 minutes. The attackers will then have to "clear the base" themselves instead of relying on the ack instantly popping and doing it for them.
Also, by keeping the ack down, the side that lost the base now has a better opportunity to recapture. This should create more interesting fights in the process. As it is now, most of the attackers quickly land (especially if they have gotten some vulch kills in). Meanwhile the the defender's reinforcements arrive from the adjacent base, only to find little or no fight over the newly captured field. By leaving the ack down, the attackers would actually have to think about defending their new base from an easy recapture.
This also makes the tactic of completely flattening a field, dropping all hangers and ack, more risky for the attackers. They may need those hangers to defend the base right away, since the defenders may have a recapturing goon standing by. If the hangers are all down, the attackers would have to stay up or rearm to defend, or risk the newly taken base being recaptured. (Anyone else picturing 10 vGuys on a rearm pad with no CAP up...?

)
The bottom line is this may lead to more fighting for a base and creative game play with regard to field capturing/defense -- a positive change from the "horde smash and quick land" (with as little "fighting" as possible) that happens over and over ad nauseum now.
My vote: Keep ack down to keep captured bases in play.
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