When I began flying, in the early 90s, sectional charts and VORs (and dead reckoning) were still the method of navigation, and that is what informs my post. I can't knock Real Plan. One thing I never took into consideration in those days was altitude selection of the favoring winds (owing somewhat to lack of accurate predictions from that age), and the possibility that an indirect flight which favors the winds might be better than a direct flight. I mean, it was certainly obvious that this was a possibility, but the information was not only unavailable to the pilot, but also whether their gamble paid off wasn't known until you completed the flight between two waypoints and discovered whether you got there more quickly or slowly than planned -- GPS speed vs TAS does this today instantaneously. So, I believe in the promise of Real Plan. Insofar as inaccuracy of GPS, I believe I acknowledge that in my post, and suggest inflating the airspace by something like 1.3 orders of magnitude greater than the standard GPS inaccuracy (which I believe is 50 feet, presently). GPS is inacurate in that it has course granularity (i.e. only within 50 feet), or not enough satellites may be visible (at which point some devices guess, based on previous trends, and turn the illustrations black and white), not in that it might tell you you're in a different part of the country occasionally.
I think you may be wrong about ADS-B out. My understanding is that without a squawk code, the N-number is anonymized for controllers, but the FAA has it nonetheless. However, that isn't something I read on a government website, but rather likely the result of pilots running afoul of the FAA, then brainstorming about how the FAA knew, and deciding the N-number is going out anyway -- the rumor mill. And, it seems to me this kind of makes sense from a controller standpoint. The controller only needs the N numbers of the aircraft they have control over. If you populated their screens with N numbers of aircraft not under their control, they have no way of distinguishing who they can vector, and who is just a flying obstacle near their airspace. At least in the near term, the controllers don't need the extra noise of displaying N numbers (even if you played games with coloring the number) for people outside their control. Probably a tell-tale change on the controller screen might be if the aircraft type floated along under the 1200 squawk code. I'm not saying it does, I haven't seen what radar looks like since ADS-B became a thing, but having any sort of intimate knowledge about the aircraft while it's "anonymous", would confirm that it only appears "anonymous", perhaps for the benefit of preventing controller confusion, and keeping "noise" off the controller's screens.
I will say this, the CFI who had her license pulled for flying under a bridge was clearly NOT squawking anything other than 1200. She didn't know her transponder was off until she contracted, I believe it was, Cincinnati approach. If she where under any sort of flight following, then a controller would have been asking her where she went when her tansponder quit, instead her her learning it was off on approach to Cinci. Nonetheless, the FAA had her ADS-B information right up until she got to that bridge. I think it's a pretty safe bet, if your ADS-B is on, the FAA has your N-number. They may not isplay it on controller's screens, but that's for safety, not because they don't know who and where you are.