User blog comment:The ASL Pirates/4th Gear & Marine Ranks/@comment-1604252-20150316011935

Maybe Luffy will unveil the ability to use his second and third gears at the same time, but with far greater control. He used it once before, so I feel it would make sense he could do so again, given how much control he has over his gears now. But I don't think something like that would be revealed at this point in the story.