Well with the campaigns being added and there only being two of them I assume that the devs would be wanting to add more and to me it at least a drifting campaign seems like it would be one of the easiest to add as it would require no AI many maps already in the game could be used for it and there's already a scoring system for it implemented and drifting to me at least is one of the most fun parts of beamNG, and as for little gimmicks for each stage you could do things like drifting through the narrow bumpy roads of small island usa or JRI, offroad drifting, or FWD sliding. There could also be various limits or restrictions, for example having to do a lap in a certain time limit, or having to score a certain amount of points in a limited time. There could even be just time trials where you use a drift car.
I totally agree with this, since i mostly just do drifting when i play beam.ng. Btw, what controller do you use? Here's a little pic with my tuned ambulance