The only developers capable of making it is union workshop but they are going nice and slow with tadami. Making a really long high speed route might be too much work since that journey would be over quick going that fast. But there are no plans to make japanese high speed
OP also needs to put forward a particular section of route, its era and the particular type of Shinkansen train. I have one of the Shinkansen routes in TSC, also a Chinese High Speed line and TBH gets a bit boring just ragging along high sided viaducts or tunnels. As Renne comments, so far as we know UW are the only associate working on Asian projects and we still don’t even know when Tadami is likely to come out. I suspect the next Japanese project, if they do one, more likely to be a commuter route from Tokyo, Osaka or Nagoya. Maybe one of the old favourites from Densha de Go.
