I disagree. I think there is a more important problem. If you're flying direct
routes and RNAV with GPS as primary(and only random route) source of
navigation, in the event of a GPS signal degradation, you have a bit of a
balancing act to do to get back to "legacy" navigation.

Maybe you do. I don't. I have a LORAN in the panel. Entirely
adequate backup for anything short of a GPS approach - and non-GPS
approaches are generally single-navaid dependent and not backed up, so
no step backward here. In general, when I'm going direct to a
waypoint, my LORAN and GPS both point to it. Either one can fail and
it's no skin off my nose.

I am not a fan of the whole intergrated-system concept. I like the
idea of separate boxes, different software, and different signals.

The perfect redundant RNAV solution is already here. It's an M3 IFR
GPS and an M1 LORAN. Same UI, same form factor, great redundancy. I
believe you can buy all the parts for less than $3000. Add a VOR/LOC
receiver with GS, and you really don't need anything else for effective
navigation and redundancy.

Michael