Plus the fact we have not seen Sulong forms of neither Pedro, Pekoms, Bepo, nor Faust indicates that there is a possibility of it being displayed in a future arc. Why create a moon transformation never to be seen again until EoS big war on a convenient full moon night? My bet is the Vegapunk arc in Emerald City (Wizard of Oz theme). Germa 66 (MADS) would be reintroduced to the rest of the Strawhats with Ceasar Clown (hopefully with Pedro and/or Pekoms the lion). Faust (and Hawkins the scarecrow if he's still alive) could make a return to explain why he was not in Wano. Law has interest in the D clan and surely Vegapunk can enlighten them all of the meaning and history. So Law, Bepo, and the rest of the crew seems likely in the mix. Kid the tinman and his crew are rivals to Luffy and need to experience what's necessary on the road to the One Piece. Emerald City may rival Wano in chapters and importance.