So let's say Blizzard instituted a Goblin/Gnome only Tinker class that implemented mechs;
+Offered a new physical ranged DPS spec
+Offered a healing spec that used science instead of magic
+Offered unique travel forms similar to the Druid class (i.e. your mech transforms into flight mode or sea mode)
+Offered mech gameplay where the Gnome/Goblin can remain in mech mode permanently
You really think they would be the least played class in the game? Considering that the mech removes pretty much all aesthetic issues people have with Goblins and Gnomes, I don't see how that would be the case.