Making a capture point neutral

So you mean... you want a RED cp to go neutral when BLU caps it?

I'm sure you could do a Logic_auto with an input from the cap point to trigger it when someone captures it, then an output of ontrigger set cap point team to neutral. Try that out?

You can make it so that a single team does not win by owning all cp's for attack/defend map play styles but i am not sure about both teams.

It's done in the team_control_point_master, take a look at control_point_round as well that might be of interest to you.

But what i can only think of is having a hidden cp below your map or something which is hidden off the hud (controlled in the flags menu of the team_control_point). So that not all the cp's can ever be capped. It's a bit make shift but it may well do the trick.