Definitely the low population is because of the split community. Apart from racing in the UF BabyR tonight, I've barely launched X10 myself!
The entry level Single Seater server is initially going to alternate between the FBM and the FOX, in the same way the GT2-R/TBO servers have operated for the last few months. I'm not anticipating much of an issue with departing drivers in this server, however, because the FOX and FBM are not radically different types of cars to drive.. most people I know will happily run either the FBM or the FOX, simply depending on which car is available to drive. If that turns out not to be the case, however, then it's a simple process to kill one or split the server into two.