Concern about resource load or design complexity stemming from a free-roaming system of roads can be resolved by specifically choosing uninterrupted sections of road rather than a single contiguous path, or could be dealt with by slightly modifying the road at points where there is an intersection in real life. Furthermore, there is no requirement that the road even exist in real life, opening the developers up to a vast realm of fantastic possibilities limited by their imagination only.
In fact, GT already does do this, the Eiger is a great example. In fact, it is a mountain road, and has great potential to be just what we need. The problem with the Eiger Nordland is that it features spectators and race trimmings, it is a small, closed loop, and the focus is not on the simple pleasures of beautiful views and the joy of methodically dissecting a complex and unfamiliar mountain road with a scalpel of a car. While it is a technically demanding and challenging course, it is an impersonal, generic, competition oriented implementation of the concept of a mountain road.
If the GT team is ever to successfully introduce the kind of roads we are discussing, they must also recognize the very fundamental difference between such an experience and that of a competitive race. While a poorly arranged series of curves can still be boring, attention must also be paid to novelty - while most tracks are quite uniform in their format, the joy of a driving road is in it's changing form as you pass through it. I would expect patches of loose sand and gravel, more strongly terrain biased turn banking, dramatic elevation changes, and far more attention paid to the surrounding scenery and organic environment. The necessity to push one's self nearly to 100% of their driving ability in competition makes it a lot easier to ignore the background scenery and fine detail of a road. Without this pressure, people's eyes will be far more likely to pay attention to detail and appreciate the effort the developers have put into the entirety of the world.
Quite frankly, while I'd kill for this to happen, I don't think the Team is ready to deal with that whole new side of the game when there's so much still to improve in the existing game.
Eventually we will see a move in this direction, the appeal is there and the concept fits neatly into the original philosophy of the game, however I wouldn't expect it any time in the near future. And I say that with the fervent hope that I am 150% wrong because I would like nothing more than to see it happen.
didnt realise. 
