There's been a lot of talk about file size and cartridges and now we have official word.
https://www.engadget.com/2017/09/13/doom-2016-nintendo-switch/
Edit:
MORE/CLEARER FOOTAGE FROM JAPANESE DIRECT
https://www.engadget.com/2017/09/13/doom-2016-nintendo-switch/
Bethesda told Engadget that the Switch port of Doom will have all the updates and DLC released for the original game except for the SnapMap level editor. It's also worth noting that the physical version of the game will only include the single-player campaign on the game card due to size constraints -- to play online multiplayer, users will need to download a free update. Naturally, users that choose digital-only copies will get the whole package in one go.
Edit:
MORE/CLEARER FOOTAGE FROM JAPANESE DIRECT