Not saying it's necessarily going to be a pirate/seafaring themed expac, but I think there is some circumstantial evidence indicating this Stormbreaker leak is real.
1) I think it's highly unlikely someone randomly pulled Carrack Escort out of their ass to build hype around their leak. Most would not recognize a carrack without Googling it. I think the leak being real is a much simpler explanation.
2) The Waveborne Diplomat’s Regalia and Solemn Watchman's Garb are both nautical themed. The Solemn Watchman's Garb is less obviously so, but I think it resembles a conquistador or nautical explorer's armor. They were also both pretty random inclusions, and they don't give off the same "rule of cool" vibe as other shop transmogs (especially the Solemn Watchman) so I have a feeling their assets may be used in the next expac, or Blizz is hoping they sell better once it is revealed they are themed to the next expac.
3) If Wrath -> Shadowlands and Cataclysm -> Dragonflight it's time for MoP -> ?
The Wondrous Wavewhisker mount is 100% going to be reskinned and used in the next expansion, and I suspect it is going to be a Jinyu mount. I get that it's used in 10.2, but Blizzard would never invest that amount of art resources into a shop mount that is only going to be used in 1 zone in Dragonflight.
This same pattern is true for the following shop mounts:
Heart of the Aspects released in Cata -> assets used in Mop
Dread Raven, Iron Skyreaver, and Enchanted Fey Dragon released in MoP -> assets used in WoD
Mystic Runesaber released in WoD -> assets used in Legion
Vulpine Familiar and Sylverian Dreamer released in BFA -> assets used in Shadowlands
Sapphire Skyblazer and Nether-Gorged Greatwyrm released in Shadowlands -> assets used in Dragonflight
I think it is a very safe bet that the Wavewhisker assets will be used in the next expansion. Whether that's indicative of a water-themed expansion is another story.
Also, as far as the globe on the leaked logo goes, it could just be in midanimation (spinning). Maybe they animated it to pop in this time. Maybe the whole world is underwater? Who knows?
All just speculation obviously, but I think a pattern is forming.