that is true but at the same time, now that he has shown us, we can make certain lvl of assumptions.... and I agree that except for giant luffy i dont see a 4th gear. maybe Luffy-Bomber! lol
Maybe he'll combine Second and Third Gear...
*Insert witty remark here*
"Bankai, Senbonzakura Kageyoshi" - Kuchiki Byakuya, right before he's about to **** you up
Orochimaru for final villain!
Normal Luffy is gear 1st.
Perhaps the 4th gear consists of the following: Luffy consumes a chemical stimulative from Chopper, temporarily increases his blood flow, self production of Isoprene and kinetic energy. The result increases his rubber body's dexterity, flexibility, stretchability. Breath dials pump nitrogen and oxygen mixture into Luffy's bone structure, effectively fasten the isocaloric process and hardens Luffy's rubber properties and fixes Luffy's gear 4th structure.
The result is a giant Luffy with above average movement rate. That is gear 4th. The side effect is that Luffy loses his stretchability after deactivation for several days, due to the abnormal isocaloric process that hardens Luffy. More over, instead of Chibi Luffy, Luffy will slowly shrink from giant form till normal. Isoprene is also considered a a human carcinogen. Thereby Luffy will be more likely to have cancer in the future.
Mugiwara Pirates on drugs, awesome. To me that's kind of lame, taking steroids is Chopper's thing. Luffy consuming something like that to make him stronger doesn't seem likely to me, unless of course he ate it by accident.