Disagree here. I would say Tinker suits a South Seas xpac well, as much so as an undermine xpac. Any South Seas xpac is going to feature the goblin cartels heavily- it would be a steampunk-pirate xpac. Naga can also be very tech-themed, remember their giant steam powered water works facility in Zangarmarsh. A South Seas xpac would also involve iron clad steamboats, zeppelins, submarines, etc.
In my opinion, a maritime-only or tech-only xpac would be a flat, mixing the two enhances both and meshes well. This concept also works for an Undermine xpac (gnomeregan, drills, dark iron tech, etc), and perhaps also a legion xpac (fel engineering, magitech, ethereal void science, etc). Emerald Dream, not so much.