I asked a friend (see mcdonalds link in my sig) about his car, and his next car he'll be driving. His Porsche doesn't have a fuel guage, and the fuel is calculated by the teamchef, and if he thinks they'll run out, they call the car in to the pits. Unfortunately he almost ran out of fuel once, so he's against this way of working.
The next car, a Renault Clio, DOES have a fuel guage and light, and because this is much better, he is asking the team to install a fuel guage and light (a reliable one!) also, in the porsche. So I think more and more modern race cars do have these things, so LFS should install them too, maybe as an option?