when no one else is in a PVP server allow the first player to wander the map until someone joins
maybe add toggleable bots that disappear once someone joins.
The only way to get a server started is by having someone wait for others to join once they see someone is on it. (I also know this is partially caused by player count right now.)
I write this because i really enjoyed the chaotic fun and genuine fear of the enemy team running down a hallway towards you while your alone trying your best to figure out if you should try and ambush them or if you should just get out of there.
Hazardous PVP Game mode
Normal PVP but with map hazards that can include random monsters or a center area with area control features that can change the layout of certain parts of the level (this level could take place in a training sector of some kind with the control room being some kind of hard point that both teams want to take for their own to try and take advantage over the enemy.
This second suggestion here is an idea that might not be able to be implemented into a game of this tone and maybe too unreasonable to implement.