I use it but not sure if as intended? What I do is I have one large track library on my SS Hardrive Then I just make various tracks.set files like tracks2014.set tracks2012.set tracks1999.set etc......
They all draw from the same library of tracks so I do not need a bunch of wads or directories with duplicates. Maybe this is the same as what your describing anyway? Not sure but I like it a lot & allows me to make seasons in order as actually done I just use a F1 site to get the info order etc.
I use this feature for my own 2014 Mod. For some tracks I have created a own wad file, e.g. cars_silverstone2001.wad which is stored in the GP4 main directory, for other tracks I reference the wad file I want to use in the /gpxdata/gpxtrack.ini file, e.g. CarsWad12=cars_silverstone2001.wad