The idea is just plain unnecessary honestly. Why does he need a full body fire anyway? Sanji's hell memories already makes the mera mera that much more insignificant. Luffy only fights with his arms and legs and im sure he can ignite fire with those parts by now , so why go any furher? I dont even see what a full body 'red hawk' can do that a regular red hawk cant. Its stupid i wouldnt want to see it happen , especially as form for G4 since he already uses flames in G2.