I'm pretty skeptical of the Ryuma will be relative to Joyboy thing. We know Ryuma protected Wano from the world government, but it hasn't really been implied he ever left Wano to participate in the great war with the 20 kings, and if Soyboy had an ally from Wano, it would most likely be a Kozuki. So, I'm not really sure we will even get a flashback of Ryuma or anything.
Also, Kaido and Oden never really talked about or cared about Ryuma much, they just talked about Soyboy coming to Wano and how important he is. Even the Gorosei never really said anything about Zoro looking like Ryuma or whatever, it doesn't seem like anyone important really cares about him, only just average people in Wano.