I know how it is with Microsoft and Bethesda, generally speaking, but no, Sea of Thieves is a multiplayer game. I don't think that game effects what Bethesda is going to work on. Bethesda has two big projects as big or bigger then Fallout 4 and Skyrim, we know this, its been confirmed. We also know we will hear about these games most likely before TES6.
So TES is a fantasy setting, and Skyrim wasn't a seamless game, by any means. Fallout 4, not a seamless game. Just about every interior in Fallout 4 has a load screen. In Skyrim this definitely true. Todd Howard said it will make sense when we see these next two projects in the works in regards to TES6. He said they don't have the technology right now for TES6. Whether that is the case or not, I don't know.
However I think that at least one of these next two big projects they are working on are running on entirely from the ground up engines. Are totally seamless games, no loading after you load into the game. Are open world, and I would be very surprised if one of these projects is not a straight 1700's+ Pirate themed game. Its a wild guess, and a hopeful one.
My logic behind my wild guess, is that we have Fallout (wasteland), we have TES (fantasy rpg), and then we have these games like Doom, Dishonored, etc. Its confirmed the games are as big or bigger of projects as Fallout 4 and Skyrim, so you haft to think what would you do as Bethesda if you haft to make a game with the production value of Fallout 4 and Skyrim. With kind of the mindset that these games are kind of benchmarks or stepping stones to TES6.
I think its without question a brand new engine, that Bethesda has never used before. It will be this generation we will see it, and could very very possibly be announced this year. I think that game could very well be a Pirate open world game of some kind, maybe with added fantasy elements in it.
I am very positive it will not be a linear game like Dishonored, these are two huge projects. One of the games could very well be a sci fi game as well. However I am hoping, and would not be surprised if they are in fact working on a Open World Action Adventure Single Player Pirate game, of some kind.