I backed the game through Kickstarter and purchased a couple copies. As a Kickstarter Backer I’ve also seen that I can redeem my Chaoseater Sword backer reward.
When I redeem this reward, will it function in both copies of the game? (say, in Steam on my Mac, as well as my future Nintendo Switch copy?)
I think it’s confirmed that the Kickstarter backer codes are universal across the game’s multiple platforms.
You should be able to use it for Steam, Mac, and your future Nintendo Switch copy without issue.
Thanks for the reply @TheFourHorsemen!
I was directed to post here “as our devs are in there able to provide you with technical solutions.”
Was hoping to hear an official response.
Worst case scenario, I’m back to contacting support when the Switch version releases. 
Sorry for late reply, my bad.
Just tested the Kickstarter backer codes on the Steam version I have (when I was beta testing) and confirmed that the Kickstarter backer codes are universal across all versions of the game.
Once that Switch version releases, you can still use those backer rewards codes no problem. 