I think it would be nice to allow individual maps to set a 'reversetrack' flag, which would allow users to race the map in both original and reverse mode.
For example, with 'reversetrack' activated the original last checkpoint would become the new starting point and the original starting point would become the new last check point. It may be necessary to also allow a 'reversestartposition' that would specify the alternative starting direction of the car. It will also be necessary to provide a mechanism to select in which direction to race a track: the original (as intended by the author) or reverse (from original last checkpoint to starting position). Perhaps the 'choose car' screen could be hijacked to allows selecting the race direction before the start.
The obvious advantage is that this would instantaneously double the number of maps available from the current 20 (not considering Events) to about 40. Some tracks are not meant to be raced in reverse, usually because of some big jumps. But most could, and personally I'm often quite curious about how the track would feel when racing it in reverse direction. And unfortunately the (small) cost of cloning an existing map and manually reversing the checkpoints has always proven prohibitive to me. And it seems that it should be easy enough for Trigger to parse slightly differently the *.level file when the 'reverse' option is activated.