Kuzan was with BB or not?
He could have left!? It really depends on how much Oda wants to stretch Egghead island. If Egghead is meant to be a long arc (which I don't think so) then adding more characters–especially powerful onse–is the right way. If both Blackbeard and Shanks come to Egghead then we are looking at medium length arc. But considering the fact that we are going to have Elbaf which is looking like to be an even bigger arc than Egghead, then I think Egghead is meant to be a short arc. Plus, so far we've seen Blackbeard sending his crew members all over the new world for stuff, I think Shiryu and Kuzan are great additions to this arc. We can see Kuzan and Kizaru interaction, Zoro and Shiryu interaction. Plus Garp is going after Blackbeard, it would be strange if Blackbeard comes to Egghead when Garp is heading to the Pirate island.