The following comes from a Reddit AMA with Dittomat, the dev behind the game, and RawFury, the publisher...
On the ease of porting to Switch
RawFury: For the porting, we worked with a team called Coatsink. They had the game up and running quite early and did a stellar job on the port. The big challenge was ensuring a solid 60fps without sacrificing gameplay or art.
Nintendo have been great to work with. They've been very supportive throughout
Dittomat: Coatsink helped out with the porting. I'm pretty terrible at optimization and stuff, so I don't know what I would have done without Coatink and Marty especially that handled the heavy lifting there!
Working with nintendo was very interesting, I've been a nintendo fan since I was a kid, and it's really really cool to meet a couple of the people that are maybe usually behind the curtains for a lot of people!: )
The porting itself isn't too bad. There was a LOT of optimization and fixing to get it to run smoothly at 60fps tho. Nintendo was very helpful throughout the process, and helped out whenever we had problems! :)
Raw Fury, our publisher, got signed as an official Nintendo Publisher (how that works is super secret tho, I think it involves blood sacrifices?) so I sort of just lucked out in getting the opportunity so early on in the consoles lifetime! :)
On Switch-exclusive content
Dittomat: The version that is on Switch right now has new enemies in each world. These new enemies won't appear unless you're playing really really well tho, to like.. balance the difficulty to make it even harder for """pro players""" :D It's also got some finetuning on the combo system, some visual effects and sound effects! :) That version will eventually come up on Steam as well, but I want to let it sit on the Switch for a while first! :)