I’ve just encountered a major issue when I was working intensively on a site and unbeknownst to me another admin was also working in Microthemer. I thought it odd that Microthemer was flipping back to a different class. It them wiped out my recent changes. The other admin experienced the same thing with the end result we both lost a lot of work.
Perhaps there could be a warning and lock the same as for page editing in WordPress?