Unnamed sources have Kuroda as a front-runner.
Haruhiko Kuroda is head of the Asian Development Bank, his term runs for another four years.There is some concern in Japan that if Kuroda resigns early a Japanese may not replace him as head of ADB.
Kuroda is firmly at the dovish end of the spectrum.
There aren’t many further details, but some extra here:
Japan Times: ADB’s Kuroda emerges as possible BOJ chief
Asahi Shimbun: ADB’s Kuroda front-runner for next BOJ chief