I have tested the new pi3 B+ using the picroft image. Unfortunately it doesn’t work as it looks like the new hardware is not supported under the old jessie image. raspberrypi.org have released a new raspbian distribution for the pi3 B+ but it is based on stretch. As of now mycroft doesn’t appear to run under stretch so I wouldn’t recommend rushing out to buy one of these new boards. For those wanting to try out mycroft but don’t have a pi yet, you will have to make a decision whether to buy an outdated board or wait and till there is a mycroft image that runs under stretch (or maybe the new hardware bits can be backported to jessie).
Note this is based on my experience YMMV,