It's not for freight. The porposal is about inter-region.passenger traffic.
geographically, probably, operationally, I don't get it.>Freed up capacity on Tokaido Shinkansen after Chuo Shinkansen is for Shizuoka with Tokyo, no room for this.
Trains entering Tokaido Shinkansen from this branch continuing westward will still serve rest of Shizuoka, and allow Shizuoka resident to have more convenient access to rest of Eastern/Northern Japan. Other trains will still continues from Nagoya through Shizuoka to Tokyo, or start from Shizuoka City to Tokyo, it shouldn't cause much different.
This os essentially a quadrupled track version of Tohoku-Tokaido Shinkansen between Shizuoka and Utsunomiya which focus on through service between two area and bypass Tokyo, with connection to Hokuriku and Joetsu Shinkansen, as well as connecting those peripheral cities at the edge of Kanto area together