I never really liked the smoking guns menu. The PB2 menu has already been remade once (very early on like build 3 or something, most people won't remember how terrible Q2's was). I can see why there wouldn't be much motivation redo it a second time.
I wouldn't mind seeing a new hud, and config file support for custom huds. I took a shot at porting the hud code from warsow to pb2 a couple years ago thinking I could do it in a few days, but determined it would be easier to write one from scratch.
A big -1 for "realistic" physics. For me the movement of this game has always been the single biggest attraction and can take years to master. I'm constantly impressed by the evolution of jumps, seeing stuff that wasn't thought to be possible for the first time.. and then seeing most clans being able to pull them off in matches just a couple months later. It's about the only thing keeping old maps fresh.
On the other hand, I could see a speedball gamemode being popular with the newer players and people trying to find a paintball simulator. Kill the strafe jumping, slow down player speed, maybe add in sliding and a stamina bar. HLDP was actually not too bad, it just never quite have the polish and the gameplay needed some fine-tuning.
Speedball maps would be super easy to make, just drag and drop a few prefab bunkers onto the screen and mirror.. stuff that could probably be done within the game itself or even changed dynamically on the server. Imagine being able to export a bunker layout to a text file, uploading it to the server and have a unique map for a speedball tournament.