I really don't get the lack of hotseat. One would think that the game would see a human player and their moves exactly the same way it would the AI's, so I have my doubts as to whether it's due to any sort of technical limitations. Plus, if your Switch is having to monitor your opponent's moves and progress on their Switch/copy of the game, it's pretty much the same difference as far as strain on your system's resources. I have a sneaking suspicion that, like so many other (overwhelmingly negative from gamers' perspectives) developments over the past few years especially, it's more about the business model...in this case forcing consumers to buy an extra Switch and copy of the game in order to be able to play together.
Firaxis/2K probably can (and SHOULD) patch in local hotseat multiplayer for the Switch version, because they're killing one of Civ VI's biggest potential selling points: immensely fun local multiplayer. A lot of (if not most) folks don't have friends with a Switch, let alone another copy of Civ VI; offering LAN play as the only multiplayer option is simply a broken concept.