i think a good hog map would have to be symmetrical in both base layout and map layout. i think there should be 2 hogs per base and the map should be small enough so that the other half of your team not in hogs can still operate but at the same time big enough for hogs to roam. the reason behind 2 hogs is that they die very easily and that can add a kind of hog to hog teamwork and make the game more interesting.
as far as weapons go i like the idea of a neutral plasma launcher, with that there should also be maybe a concussion rifle and maybe a man turret to aid in hog suppression at each base. i think you should omit adding snipers, rockets or lasers as they tend to give a heavy advantage to a team wielding these power weapons.
as far as vehicles besides the obvious 2 hogs per side i think each side should get 1-2 mongeese. there should be no air or heavy vehicles to keep the game fun.
last thing i could think of is that all except a few should be outside the base, similar to how standoff had it with brute shot and invis. this is because a reach hog cant take 3+ enemies like a halo 3 hog could. making all the sapwns inside would make it hard to get kills, but placing them outside would allow the hogs to do some work but also with the fact 3 people teamshotting DMRs at a hog will make it think twicr about sticking around.
just my 2 cents
EDIT:you could also get creative and make a map using
waterlike this guy did