with a q3bsp shell thing
What's that?

I mean, I know (partially) what q3bsp is (it should be the Quake3 map to bsp compiler, right? - but I can't distinguish it from q3map2), but I completely ignore what is a "q3bsp shell"!

wait, for shell, do you mean shell command? Like a q3bsp command sent via command line? So it's something that is precompiled, not dynamically created at runtime, right?
you can then use the openportal builtin to open/close the portal between the two areas
I searched for "openportal" in csqctest but I didn't find anything. Sorry but I couldn't find it.
if the portal is closed, vis is blocked too. lights behind the portal will no longer be drawn. this is what q2/q3 use on doors to dynamically close the pvs.
Sure, that'd be great!
the 8*8 grid is because there's a limit to the number of areas you can have. in theory I could boost it to 256*256, but that's a loooot of memory, and even more entities to track the portals (though I guess with q3bsp you could just use setorigin to find the two areas dynamically, which might help reduce the number of entities).
Well, it could be fine. I just delete every sector far from player, once the player left the "
neighbour sectors" (grey squares)
Tonight I had an idea: to avoid that other players could see different sectors I set a rule. Once the game has started, first player connects (this maybe will be a little complicated to code) is the Leader. Other 3 players (for a total of 4 players like Left4Dead)that connect after him MUST follow him and don't lose him! If a player is outside gray bounds when the player run, he dies. So game will be DEFINITELY a coop mode and every player will see the same group of sectors!

What do you think guys?
EDIT: I was thinking... but if I delete the group of sectors when it's not needed anymore, lights would be deleted too, right? So the light computation would be always of 3/4 rtlights into a 512/1024 environment at time, right?