Patch 7.2 introduces new epic class flying mounts with the legion flying unlocked. Each class with each spec will have its own exclusive epic class mount. This is a unique look and full of class specificity of the epic mounts, which can be fully displayed for each class's characteristic. For example, Raging Tempest Totem of Shaman, Decaying Reins of the Vilebrood Vanquisher of Death Knight and so on.
Is there anything better else to fly on Broken Isles? 
Two factors need to be done as follows.

1. Unlock the Third Relic. the old campaign quest, Unlock The Third Slot For Artifact Weapon. 

2. Breaching the Tomb. New class campaign. There are 11 quests in total which will refresh once at each week. 11 weeks can be completed. But it has a pursuing system, you can complete it all quests at once time after the 11th week.

Each class will gain their own unique talent flying-enabled class mount. If you like the other spec mount, you can purchase it by Order Resources after completing the Power Ascended achievement. this achievement requires unlock every Artifact Trait for a single artifact weapon after empowering it. Also, you can buy the relative pets and toys for each class. I think that everyone can unlock all traits in 11 weeks.
Flying your own special class mount on Broken Isles, that must be very cool.