So one of the issues people have with the inclusion of Tinkers as a class is how they would fit into the grand story of their intro expansion. DK's had arthas as the villian, Monks had Pandaria, DH's had the Legion. Now how can Tinkers be introduced outside of a goblin and gnome centric expansion. Well I think I figured it out.
Now the Dragon Isles were name dropped for the first time in cannon lore during BFA by one of Wrathion's goons who stated Wrathion has been searching for them but other dragons have not come clear with any info.
So what if the they are hidden via titan technology similar to Uldum before the Cataclysm?
Well after 8.3 Wrathion has made himself new a friend in the form of MOTHER and acquired multiple dragon essences used to empower the HoA, similar to the dragon soul.
So what if... Wrathion decides to visit Undermine (which will serve as 10.0's main hub), which has yet to be added to WoW, gather the world's best Tinkers under one roof and combine their tech with MOTER's titan tech, and wrathion's draconic essence to locate where the titans hid the dragon isles and create a means of transport.
With successfully helping Wrathion locate the dragon isles he funds the Tinker's Union and they're able to spread their influence even more across azeroth, giving birth to the next playable class.