Said silhouette image resembles Yoh Asakura's appearance in the first compiled volume of the Shaman King manga. June 2018 will mark the 20th anniversary of the Shaman King manga. The author previously teased back in October via Twitter that he is working hard on a new project, and fans can be relatively certain that a new Shaman King manga sometime next year. Shaman King Flowers concluded its JumpX run with a total of 24 chapters with a cliffhanger and a lot of plot threads left hanging.
[Source: Anime News Network, Crunchyroll News; additional info: Patch Cafe]