It will be through services between all four different lines, Joetsu, Hokuriku, Tohoku and Tokaido.
It will be done only after the introduction of Linear Chuo Shinkansen, which free up capacity at Tokaido Shinkansen line, and inteoduce room to operate more flexible services.
It remain to be see whether JR Central is going to keep their capacity specification requirement after the opening of Linear Chuo Shinkansen.
As for being 土建国家, Japan is actually much milder than like China or even South Korea. In Japan there are still plenty of viable routes with B/C ratio potentially over 1 not getting any attentions.