Don't you think it's a little too late for this alleged reappearance of Hiori?
If Luffy, Momo, Yamato had just started the final fight already - it would be a bit weird and forced of Hiori to suddenly appear. We have no idea what she is doing or where she been for a very long time and suddenly BOOM - Hiori was here all the time.
My greatest fear is that Hiori will save all dying samurais. PLS GOD NO