With regard to the comms failure - when being radar vectored according to the rules we wait 3 minutes and then return to the flight planned route. (UK local requirement).
However, we have been sent to a point on our flight planned route whatever miles ahead. This suits us and suits ATC. One could argue that we are not being radar vectored we are simply agreeing with ATC that we will maintain the heading that is currently taking us to that reporting point. Thus we would in effect maintain the heading for 3 minutes after R/T fail and then if necessary adjust heading to maintainn the track to that reporting point and thereafter follow the filed route.
As for the problem with fly-by waypoints. There is nothing new there. It is not only modern aircraft that can take advantage of that - old steam driven aircraft can also (and have done also) in enroute airspace.
Remember that when enroute we navigate to RNP5 - we must remain within 5nm of the route centerline. Thus the aircraft can at any time be up to 5nm to one side of the ATS route and still be considdered to be navigating to the required accuracy. When at a turn point (intersection or beacon) it is perfectly allowed for the aircraft to "cut the corner" or "anticipate the turn" or whatever one likes to call it provided that the flight remains within the requirement of RNP5. Imagine leaving a 90deg turn overhead a VOR until the VOR indicates station passage as say M.80 and FL350 - how far would that put the aircraft off track initially!!!!
I believe that is one of the reasons why radar controllers lock aircraft on headings to ensure radar separation.
Regards,
DFC