Hard to say, if he has it hypes us GB but then that haki blast from Shanks and GB's reaction killed any hype at all. Would be nice contrast to Fuji's CoO, if and it's a big if, CoA is required to make black blades. Don't think he should have taken it from somebody else (kind of de-hypes GB and we have probably another legend like Ryuma, too late in the story for that imo). Would be one of the most powerful and versatile guys out there with that crazy df on top of a black blade.
Personally I don't want him to have a black blade, feel like it will become the new ACoC where everybody is having it now like SSJ in DBZ.