Totally agree with your points Hawk, having un-licensed replicas of tracks that are licensed elsewhere won't bring people to GPB, which is why I'm suggesting something that isn't seen in another (or many) sims, something different to make it interesting.
GPB must also stay true to its vision and scope, though.
Modders are, of course, free to do whatever they like, but at the core GPB is a simulator about relatively modern GP motorcycles. Therefore, the stock tracks should be real circuits that hosted the GP championship in recent years.
I wouldn't be so sure about that Pib?
If you think about it, the "Classic" genre might just be what GPBikes needs to widen it's appeal? Is there any other bike racing game that caters for the true classic bikes and tracks as well as the modern genre of MotoGP? There could be a little extra niche opening there that GPBikes could appeal to?
Plus as a wild guess I would say that the more "hard-core simulations" appeal more to the older age groups than the younger "gamer" type groups.... the older generation tend to be drawn more to the classic eras as well as the modern? 
TBF, I don't know what the initial Idea was behind GPB, or what vision there was for its development path, but it just feels like there have always been games (Of varying Realism) surrounding Grand Prix Racing, and doing something different maybe just whats needed to spice up things in the market. Tourist trophy was a great game back int' day, as that focused more on racing and not GP's, and I get the impression that's one reason as to why that makes the Ride series so popular now, as its something fresh and different.
I mean if your set on going for Grand Prix tracks there are so many again that are not seen in many games/sims that could be fun to ride, like the Salzburgring, or Rijeka (Automotodrom Grobnik), or even the Brazilian track which I seriously enjoyed back in MotoGP 4, it was called Jacarepaguá or nelson Pique Circuit. Sadly it was torn up for the Olympics, but it was an awesomely fun track to ride in that game, that perhaps isn't what is associated with 'fun' motorcycle riding as it maybe isn't as flowing as most. (But then again I did a track day at donnington and thought the Melbourne Loop was the most fun part over the rest of the track so maybe I'm Just weird).
I guess the point I'm trying to make is that there are so many circuits out there that haven't been seen often before, in both GP's, WSBK, or at club level, that could really be fun additions to GPB. GPB is so different from pretty much all bike games out there in the fact that its a sim, and the potential of
not licensing tracks means that there could be pretty much any track done to a high quality, so to me it seems a shame to do something that is already out there. Both in and out of the GPB world.
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