I am all for a melee weapon/action. You could add something like a kick or a gun-smash melee action. Or add a whole new weapon, like a lightsaber kinda thing, but then only make it available to the outrider (i couldn't picture a sentinel wielding death in a lightsaber form) or something like that. As for the melee weapon's damage, well i think it would depend on whether you are hitting a Outrider, Raider or Sentinel. As well as where you strike with the melee weapon, a hit from the back dealing more damage than a hit from the front sounds good.
But then if you were to make a cloak core, the melee weapon could be paired up with it to make a kind of assassin that sneaks up behind someone. But (now i'm thinking of tribes 2 here) a cloak has always annoyed me, invisi-freaks going around killing you like crazy (I'm talking to YOU smokesoul). So maybe if a cloak core is in the future of Legions then you can make it not fully cloaked (you can still sort of see the guy if you look carefully) and have it not last too long.