Tokyo Metro has revealed the new 18000 Series EMU for the Hanzomon Line to the press, it will officially enter service in August this year and gradually replaces all 19 8000 Series sets by 2025
https://news.mynavi.jp/article/20210603-18000photo/>>1660959>Non-Saga City routesAre those options financially realistic / viable to begin with? The thought of digging tunnels towards the Saga Airport or north of Saga Prefecture seems like a waste of money