Ideas

[X-Ray_Dog]

Disable friendly fire at the end of a round.
Disable friendly fire for a few seconds at the start of a round.
Mirror friendly fire.

Fully agree.

Increase spawn time to 7 seconds for a player who kills himself.
Decrease T/OSOK ammo to 5/5 or even 5/0. Encourage knifing.
Cut shotgun's range at least by 50%.

Not so much agree. Suicide is a common thing for some players and I don't feel you should be punished further than what we have already for it. As for T/OSOK, I think the standard is fine as it is. Knifing is a skill that must be learned with it imo. Shotgun.... no. The spray increase should fix this.

I'd also like to see some "fun" modes where some variable has been changed to alter the gameplay. 5x kickback, 2x grenade radius, knives send players flying when hit. Something ridiculous and weird that will always be fun.

Insta kill CTF with sniper only aka ICTF, maybe a survivor CTF would be trolol as well. You could incorporate that with other flag modes as well or so.