Update! I looked back at Genki's twitter again, and they have replied back to quite a few interesting posts.
1: It is likely that it might get an overseas release into Europe, and USA & Canada. I'm not too good at translating Japanese to English, but Genki did agree with the comment of there being a big fanbase for oversea. But I think they mentioned there being a bigger chance if people from overseas were asking questions and supporting the game. I'm not entirely sure.
2: There is a good chance of customisable interior like there was in Import tuner challange again, as a comment was asking about custom guages, and Genki replied something along the lines of them being released at launch. I may be wrong in thinking that, it might be they are on about the gauge display on screen when not on interior mode. As I said, I'm not the best translator.
The other thing about the exterior having vast customisation, it's most likely but again they cannot confirm it. There is a chance of 'Rocket Bunny' being added to the bodykit lineup - 'Whether the selection and inclution request of models is possible, because we don't know, it depends on time.' was the reply to a bundle of bodykit manfacturers being added.
3: For the car list there is a few comments concerning the GTR lecasy, it seems that it's likely the KPGC10 to GTR (R35) are being implemented. There was also comments about foreign cars, Genki said something like, they will be increased. There is another comment asking about adding in the likes of Lamborghini and Ferarri, Genki said it might be possible, but they are planning it. Also they said more 'light cars' are to be added, most likely refering to Kei class cars. They also say they cannot 'guarantee' most of the requested cars to be added. The likes of Honda are unlikely, as Genki say they cannot answer anything about that.
4: I'm not sure on this one, but the traffic of yellow team Hiaces might be replaced with regular traffic, e.g Trucks, sedans, vans all in stock colours.
5: There was only a few comments concerning a livery editor, Genki didn't answer direcly with there being one, but a person asked if 'Itasha' cars would be an option, Genki replied they don't know.
6: Their plan on a release is still undecided from most comments asking on it.
But they do plan on it being a PS4/Xbox 1 next gen platform, and not on PS3/Xbox 360
7: There was one comment concerning police pursuits, Genki replied with something suggestive 'When dealing with police car, it's presence will determine on wether you respect the law' - Along the lines of that translation.
This is all I can find from the answered questions.
It would be great if we could somehow get a better translator than me though, as I do a on-par job with translator-san.