Elective Duel Mode:
10 minutes
Elective spawning - choose any spawn upon death or at start of round
Choice of map concedes first spawn choice
Players are able to see each others' spawn choices at start of game (this could be changed if necessary to give the map chooser more of an advantage if the spawn choice proves too strong)(Regardless, the second player to choose will know the first player's spawn choice)

Showdown-style spawn screen (don't show opponent on preview windows)
Spawns roughly equidistant from weapons & powerups (10-12 spawns), or
One spawn near each weapon (8 spawns)

Item spawn times could need adjustment based on gameplay speed...faster health/vials (15s)?
Spawn closest to last death or survivor position (@death) could be locked if necessary

Just a rough idea I figured I'd throw up here, let me know what you think or if you have changes/additions
This idea started here if you're wondering why I came up with this: