The immediate problem with slot car systems is the jackrabbit acceleration and speeds, making them unsuitable for use as a working background for model railways.
Back in the 1960s and 1970s, Faller did produce a slot-car system in HO, similar to the later Aurora racing sets, which was remarkably comprehensive. Didn't catch on, though.
Nowadays, you have the current Faller Car System, or DCCar (an industry in itself) or even remote control in 1:87.