https://tabiris.com/archives/miyazaki-shinkansen2024/Miyazaki prefecture decided to join Oita in pondering about alternative Shinkansen routes. This time the proposed route goes
>Shin-Yatsushiro - Hitoyoshi - Kobayashi - MiyazakiOn one hand, this route doesn't depend on the Oita - Miyazaki section of the West Kyushu Shinkansen, which is arguably the second least likely section to ever be built(first being San'in Shinkansen west of Izumo). It also opens the door to direct trains past Fukuoka to Hiroshima or Shin-Osaka.
On the other it doesn't cover Miyakonojo and would be inconvenient(although still faster) for Kagoshima. Also if you see Tetsubozu's video on the topic, he claims that it'd only be 15m+transfer time faster to Fukuoka than the Kagoshima - Miyazaki section of West Kyushu Shinkansen, but for whatever reason he is assuming a speed of 210kph.
https://youtu.be/-hQgy_Mf5U0And then there's Kumamoto prefecture's negotiations for rebuilding the Hisatsu line. We don't know whether they'd consider this a good or a bad thing. The repair has been estimated for 235 billion yen lasting over ten years(meaning it'll go over budget due to inflation, even in Japan), so that's not that far off new Shinkansen territory, and a Shinkansen line could be easier to convince the government to give money for. And then there's potential of bringing people from further away into Hitoyoshi Onsen with Shinkansen. I could see it happen, but I could also see none of the routes being built at all.