Sounds like id is going out of their way to make sure DOOM Eternal on Switch is getting the same treatment and attention that the other versions are getting. This isn't a port planned late after launch. Releasing DOOM Eternal for Switch was planned from the get-go. You can hear more on this and other tidbits in the Eurogamer interview snippet below, which features DOOM Eternal executive producer, Marty Stratton.
E: Will the game launch on Switch at the same time as PC, PS4 and Xbox One?
Marty Stratton: "That's the plan right now; we'll see. We're still a way away from launching but we have made the decision to make Switch a, what we call internally, 'first class citizen'."
E: So you're developing it internally?
Marty Stratton: No. We're actually working with Panic Button again, but before, we made the game and then we brought it to Switch, and now we are making the game with Switch in mind. It's nice to know the platforms we want to hit up front.
E: Graphically it sounds like you're doing even more with Eternal but you said it will run at 60 frames per second - on Switch as well?
Marty Stratton: We don't run at 60 on Switch. Doom 2016 didn't run at 60 on Switch, it ran at 30, and really it was no sacrifice to the experience.