Hi, I just tried to make a narrowgauge tram track, just setting system_type to 7, just as with regular tram track.
Obj=way
waytype=narrowgauge_track
system_type=7
But alas, it does not work as a tram. I can get it to show up in menu with: toolbar[5][2]=ways(8,7), I can build it but only on free tile. Crossing a road is possilble only as with normal track. However a crossing is not built so the vehicles on road and track do not interfere with each other. So I feel it might be partially done, partially broken, and perhaps not too much has to be fixed to get ng_tram (or even maglev_tram :) working
I'd love to see that happen
The tram waytype is rather a hack, and will not work on other waytype. It will be quite some work (well recieved maybe) to find all occurrences that assume that tram is always track.