I’ve been struggling with this all day today. So far, I’ve had to build mono from source, which required getting a few dependencies for that, which required getting homebrew to run on 10.12, and that required making sure I had the Xcode 8 beta installed and that xcode-switch was set to the beta version.
After that I tried running the promoted branch (didn’t work), so now I’m back to trying to build the release branch with all the proper tooling place. We’ll see how THAT goes.