Boot Camp Assistant: "This Mac does not support Boot Camp"
The solution for fixing Boot Camp Assistant was the same as with previous versions of the OS: reset the NVRAM.
I found a discussion mentioning a similar problem with an upgrade to Yosemite here that I intiially disregarded as it referenced repairing permissions and running a Disk Verify, neither of which Disk Utility appears to support anymore.
As for BootChamp, it is no longer supported as of El Capitan. System Integrity Protection prevents it from running.