Have flown hundreds of GLS and RNP approaches. They are the best thing since sliced bread , especially in remote areas outside conventional navaid coverage.
I 100% agree. But the cost of that technology is greater than the purchase price of your average small aircraft. F100's/EMB 120's/SAAB 340 don't do RNP/GLS approaches either and they are a significant number of aircraft on the Australian Register flying to remote areas.