ESV wasn't exactly state of art, and that even less could be said for Fallout 4, so you cant relly say that ESVI will be "modern, state-of-the-art" game, and even less that could not possible come to Switch.
In fact it was. It's not just about the visuals. The scope of the world, the AI, the underlying systems and to a degree the graphics were, in fact, pretty advanced for the time (Skyrim).
We can safely assume that ESVI will most probably will not be port-able (ha!) to the Switch.
Ok, Skyrim was sophisticated. It was *not* state of the art. Take it from someone who spent years as part of a modding team for Oblivion *and* Skyrim. Skyrim had a lot of systems and some good AI, but the groundwork of it was ultimately not that big a deal. In fact, if you want to talk about a game being state of the art relative to its day, you look at Oblivion, not Skyrim, which was, on a technical level, an insane revolution in the series with NPCs having unprecedented independent behavior, elaborate schedules, dynamic interactions. Skyrim was much more iterative on these features. And a lot of its new feature systems were of a kind that would not impact performance, such as the radiant quest system. No, the bigfest refinement in Skyrim was polishing up the efficiency of the engine and improving its visual capabilities. And replacing it's coding system with something far more intuitive. But a large part of why Skyrim was so demanding on the certain PCs was because the game was just not that well optimized. Hence why for PCs above a certain threshold get better or at least equal performance from the Special Edition despite improved visuals. The engine is much more efficient.
Honestly, unless Bethesda *finally* moves on to a new engine, you will likely see ES6 as a very similar game to Fallout 4, just polished and refined on a technical level. And I'm confident said game - if it is iterating on Fallout 4's tech like Skyrim did with Fallout 3's - could be ported.