I have been convinced sabo is alive because Oda would never make such a pointless scene with Dragon. I have been waiting like years for him to show up somewhere and this theory is just awesome. Maybe it would be a good time to make Luffy lose some fight in the new world because he beat everyone easily until now. Sabo is disguised, fights with Luffy for the Mera Mera no Mi barely wins and is like : "You really got stronger Luffy, trust Ace's power to me for now..", removes mask like a baws.