It's a rather silly suggestion.
1) Modelling this in full detail, with 2014 standards and including houses and others, would take way too much time and man hours. Could make 10 tracks with those resources, making the development even more taxing than the Nordschleife.
2) It's not worth the massive effort. As known as it is in the motorcycling world, the Isle of Man TT course is nowhere near as popular as The Ring is.
3) The PD version will necessarily have added barriers, as they have added to every single street circuit. This means it won't look and feel as nice as on those videos, which would be a pity in this particular track.
4) People would demand bikes to be in the game, which is leaving the door open to unfounded complains for years to come as most probably bikes aren't coming.
5) A major reason why that course is beloved is because of the risks involved. When racing on your couch that thrill aspect is removed, making this particular circuit lose quite a lot on videogames/sims.
In the end this is the type of content that only belongs in PC sims. By this I mean that such content is made by players -not companies- and also that you (anyone) can have access to "drive this course on your couch", right now so you don't have to wait or demand PD to make this. Please do, because the Isle of Man TT is available right now on several.
edit: I'm not saying it wouldn't be awesome to have this in the GT series. Just saying that there are limited resources and that there are some priorities to be dealt with first, such as including the classic GT tracks and some other very much delayed plans. After those tracks are made and if resources are enough for this huge project, then the Isle of Man can be done.
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