But the filter itself is a piece of cake. When the host is setting up the server, they get a box that says:
[ ] Race | [ ] Drift | [ Cruise ] | [ ] Drag
Then host as normal.
Client comes along, un-checks Drift, Cruise and Drag from the list and get a server list that matches the filters. There is absolutely no change to any of the server rules needed. The current "Cruise" category is purely to allow driving the wrong direction, it's not a client filter.