G Farris wrote:
I love GPS, and I see no problem in being highly reliant on it, because
it is intrinsically reliable - however I believe it would be practical
and desirable to build a system that maintains full RNAV capability in
the event of a loss in GPS integrity.

The big boys have it, it's called Inertial Nav. Whether that will ever
become an affordable reality for GA is anybody's guess, but stranger things
have happened. With the current crop of GPS gear on the market, there are
already spam cans equipped with better nav systems than some jets.