According to the Shikoku Henro for World Heritage website, the following properties are further along in the nomination pipeline (Category 1A) and are likely to appear on the Tentative List soon:
- The Cultural Landscape of the Mogami River
- The Eighty-eight of Shikoku Temples and Pilgrimage Route
- Amanohashidate
- Aso
- Kintai Bridge and the Town of Iwakuni
Source:
https://88sekaiisan.org/en/world/The first four are strong candidates. Perhaps even stronger than the Sado Complex of Heritage Mines and Hikone-jo nominations. These two nominations would certainly benefit from an expansion of the properties: The Cultural and Natural Landscape of Sado Island, and the Culture Landscape of Lake Biwa (centered around Hikone-jo).