FG is open source, free and open to potentially unlimited development. But humans tend to be followers and that's mainly why FSX rules for now.
But as time goes by who knows -
? FG has huge potential, as has FSX (as it is also open source)
One thing for sure. There is a demand for a realistic (as far as we can make it) flight simulator for home/personal use. By millions.
My advice is - always keep Flightgear on the back boiler ready to fire up when you fancy a change of air.
Think global. It's the world we live in