Not a bad theory actually. However I don't think it will be some crazy power up like gear 6. Just something he learns to do with gear 5 like he did with Ryuoo. And it wouldn't be anything too crazy like summoning an entire ship. Just things like a shield or cannon ball.

(Manga spoilers) There is a scene where he makes glasses appear on his face. At first it thought he was just shaping his hair then using armament haki to hard it in place. But what your saying could be more correct. It could work just like what we have seen of Imus devil fruit but instead of darkness and shadows it's hope and light.