-Leaning - Great addition. Would be nice since I play Socom and lean in it a lot, Would be easy for me to get used to. =]
-Prone - Not sure if anyone as suggested this yet or not, Didn't want to read back through 43 pages. I think you could add it as
If you press your crouch bind twice you could lay down. Or you could bind a key just to go prone. Prone and Leaning would be great together ;].
-Built in Mic Chat - I am sure this was already suggested but just throwing it out there. instead of having the Vent and Teamspeak servers, you could just have team Mic chat like you have the team chat. Key binding to talk, or voice activated. Not sure if this would be possible to do, but it's a good idea I think.
-Sliding - Like in real Paintball, would make the game more like actual paintball.