What if Gyarados got Acrobatics?
While there's not much precedent for something like Gyarados getting Acrobatics, which is usually reserved for land or sky critters, it's the most likely powerful Flying-type move for it to have as Brave Bird, etc. are obviously no-nos, and fellow Water/Flying type Mantine does get the move (although according to the Pokédex it can fly, unlike Gyarados).
Let's face it, Bounce is a terrible STAB move (worse than Fly!). Acrobatics would make a Flying Gem set very viable on Gyarados, as it can get through things like Ferrothorn before a Dragon Dance and everything not resisting Flying afterwards. Unfortunately our favorite leviathan doesn't get Unburden, which would make it the best mon in OU, but it still is extremely hard to wall, 2HKOing almost the whole metagame. However, it does have the same problems with revenge killers and status, keeping it from becoming an S-rank threat.
Although Bounce isn't the best STAB, Gyarados makes fine work of it. It's not worse than Fly, because the paralysis chance makes up for the slight loss of accuracy and power. Although Gyarados would appreciate a better STAB like Brave Bird, I don't really see how Gyarados would get Acrobatics but not Brave Bird. It just doesn't really fit flavor wise for either of them. I feel like Bounce would still be a bit superior to Acrobatics on the bulkier DD sets, because Gyarados really appreciates the Leftovers recovery. It would be decent for the offensive DD sets, but not THAT amazing. It just really doesn't fit.