Thanks to all those that helped test on the future branch, we were able to fix a few things and we're now confident enough in the new Mac build to push it to the default branch (read: Everyone gets this by default). We hope that this will be smooth for all our players on Mac (newer and older OS's). Would love to hear if it's working or not! You should see the game re-download/update. Those that hopped to the future branch can hop back to default :)
If it doesn't work, please try to exit Steam and restart to make sure you're getting the update. Then let us know if you're able to get your Dusking on :) Worst case scenario, you can get back to the pervious version by going to the "past" branch (just go to Duskers in your library, right click and select properties -> Betas, then choose "past" from the dropdown. You should see the game re-download/update.)
Hopefully if this goes well, we'll update the Steam store to make the Mac version available for purchase again :D
Thanks for all the help!