Gear 4 grants four abilities (contraction-attack, flight, elastic defense and python) and each Gear 4 Form specializes in one of those abilities:
1) Contraction of arms and legs to hit stronger
3) Elastic defense to bounce attacks back. Doflamingo was surprised when his “athlete-kick” got bounced. He said “What? Still rubbery?”. And the Tankman specializes in this technic. The scene with Cracker is almost exact, Cracker is also confused.
4) Python, changes the directions of the attacks. Snakeman is specialized in this technic. Making it faster but losing the other three abilities.
So we are still going to see another form specialized in contractions of arms and legs. And another form specialized in flight, for example:
Lion-man = Luffy’s arms and legs are huge and make really powerful attacks. It looks similar to Champion Luffy and Nightmare Luffy. But he is slow and can’t fly.
Eagle-man = Specialized in flight and speed. Great mobility, dodges attacks easily and his final attack is a better version of “Red Hawk”. It could look like a zeppelin too. Snakeman increased the attack speed but it wasn’t like Luffy was dodging easier/faster. It could also be called “kazaa-man” or “dragon-man” if Luffy has fire around him.
*Theory by CAMUNAI