I must be missing something obvious here but surely all aircraft routes nowadays are GC routes
between waypoints.
Rhumb lines (constant heading) are flown only during one's PPL training
or when being vectored by ATC. All the time one is flying A to B to C under own navigation, the route is a GC. GC is what every GPS gives you (automatically, and with no other option) and I would imagine that's what every INS/FMS system gives you too.