and you would never ever see another crew or player again since all the crews are spread across not only the giant Sea of Thieves which had its map area almost doubled with the Pirates Life update, but in addition would need to get doubled again for the idea of a giant land mass.
As you can see in several cases, the Sea Of Thieves are located in a very specific part of the real world. And of course a lot of things would need to happen before an actual big land mass could be introduced.
Old gen hardware already have 5 minute loading times in areas of high loot density. Shores Of Gold alone give people massive FPS drops on lowest settings. Can't imagine how this could ever be seemlessly introduced. Big Island but without much details maybe. But Rare does not want the servers to appear even emptier than it is right now. The original design was for players to see other player ships every 15-20 minutes or so. The bigger the map, the less likely to find someone.
Also keep in mind that Rare develops content to be actually played. I can't see how this is something that people would go to after doing it once.
Maybe as part of the PL hideout thing they promised for the Captaincy stuff back in 2018. That people can get their own customizeable hideout or even island like in the maiden voyage, but multiplayer; Crew only. So only your crew, no loot and just for hanging out in a kind of pre-lobby state. Designing your ship, decorating, maybe playing cards or anything in a hideout, preparing in a hideout before travelling into the Sea of Thieves through either the waterfall (portal) in the PL hideout or sailing through the red sea like in the maiden voyage with some kind of cutscene ending up like portal hopping. Why not?
But a giant land mass being introduced in a way remotely like you suggested is extremely unlikely if not even technically impossible due to the limitations of servers and client hardware.
It would be easier to create snow / desert themes for an existing biome and maybe a limited amount of time like during the new adventures. But then again, except snow we do have sandy islands in the Shores of Plenty as well as deserted islands in the Devils Roar biome. Not like the classical desert but deserts usually are defined by being dry due to a lack of water. See where I'm going?