I don't think there's any legal issue at play. Afterall, the Nordschlief is a public road, and there are many street circuits in video games....they could just make the entire C1 a "closed circuit", and that should solve any "don't do this at home" angles.
There's also other games like TXR, Midnight Club, etc, which feature street racing in real life locations. So again, as long as there is a disclaimer at the start of the game, shouldn't be an issue.
I think the biggest issue is the amount of data it would take to model it properly. For pCARS, the devs specificly said they didn't do any street courses like Long Beach, Macau, or Pau because of how much detail is involved. Everything from the road itself - various surface types, bumps, rises, dips, the crowning of the road, man hole covers, traffic lanes, etc, are all complex to model, and all feature different textures and grip levels. Then there's the actual environment itself. Some of the sight lines are huge, and the amount of background detail is emmense. The way light reflects off of different buildings, with all their different textures and surfaces would be complex to model. Same thing goes for all the small details, like road signs, traffic lights, street lights, mail boxes, store fronts, hot dog carts....all of that would be intense to model.
SSR5 and Tokyo R246 are actually incredibly good for a PS3 model. I think right now the options would be to stay with that size of track and increase the detail, or make the track bigger but keep the detail the same - and I think we all know by now that PD likes to stress about little details instead of turning a blind eye to them in favour a "bigger maps".
The bright side at least is that PD is aware that there is demand for this type of environment though. Hopefully this is just a start