In my opinion, if uta is in strong world and shiki is in film red with some modifications. It should be able to fit perfectly as oda can use uta's ability as not that overhype ability and luffy defeating uta by gear3 or g4 will be good if uta is antagonist in strong world . Instead if shiki is to be antagonist in film red ,fuji and kizaru coming in for still looks perfectly fine and luffy going g5 against shiki will definetly be an excellent one. Also shanks can come at last point to save SHs