So effectively, Alliance PvP.
Well, if you're going to try and push for it, may as well get a half a loaf...
I would say make it more akin to Defense mode in Alliance if you're going to do anything, either that or the final refinery of Assault. You'll have players just making max range sniping shots on the enemy defenses and main base, so it'd probably be for the best to make it more akin to the main base from Assault.
I would say, if you give the platforms any form of weaponry, remove the mines. You'd have the defenders simply waiting for the enemy to get up close to the base and start hitting the weakpoints, then just hwacha-ram them into the invulnerable base.
As for walls and drills, I don't know if that's going to add anything. Players might just cut the walls apart on principle, then attack through the open doors. Drills you'd have people just suicide ram them, hence why I said the Assault style base.
For adding defenses on every death punishes failure way too much. It's just a landslide then, and it makes it much too easy.