I think a last stand mode is a great idea, but it wasn’t executed that well in game 1. People turtled in a corner, sniping specials as soon as they spawned, and the waves came very slowly.
A new Last Stand mode should be faster paced, with ways to prevent turtling; what if you had mini-objectives, like move an object from one place to another, or hold an area for a particular wave (all still within a limited time). My inspiration here is Mass Effect 3’s multiplayer, which was a lot of fun and had interesting objectives like this to spice things up.
Waves should also come faster, and be more randomized. On top of that - no pickups at all. Give players a draught/bomb to start with if you must, but never drop anything. No ammo, no health, nothing else. It would mean that the matches wouldn’t drag on and on, but be maybe ten minute affairs - fast and furious. There’s no reason to draw it out.
I dunno if I’d want a real organized PvP mode, but I think having a room where two players can have a duel would be fun. I don’t know how on earth it’d be balanced (maybe you can choose whether nor not to allow ranged weapons). But it’d be interesting to kill some time when you’re in a group and someone is re-rolling or something.