@WhiteHare:
No, there is no preloaded image that will work on Pi3, not at this moment. The image I have is debian wheezy, and as I said before, wheezy will not work on Pi3 at all, even without any addition, will not boot, they don't even offer that any more.
MightyHat is a hardware piece, nothing to do with the gateway image. The gateway software will work with anything, even just a simple moteino hooked up to a serial port or USB.
Getting a jessie image ready is a pretty tricky task. Jessie uses boots with systemd, very different than wheezy.
I will post updates when I have something solid to share. Even the guide is probably obsolete in certain regards because it uses upstart, which conflicts with systemd. So a lot of work for me to do to update that and test it on Pi2 and Pi3 etc, i have no help, and lots other work to do.