One more idea...
Packet for detecting allowed cars. There is IS_PLC, however it is instruction packet only. My idea is to make it work both ways. Requesting info (TINY) should return PLCs for all UCIDs on hosts I guess. If connected insim is local it would return cars only for local connection. And IMO it should return subset of host cars and player cars set by IS_PLC.

That's not a bad idea. I like flexibility in general.

One thing, for every new idea, it should be in it's own thread with the title [RFC] and then a one line description of the idea.