Thanks for the reply. For some reason I thought their license an easier one to work with, but I was confused and you're right: the license is GPL.
I happen to know the Mosh team, and I asked if they have advice for using Mosh in commercial products. The reply leaves room for optimism. I'll ask
support@vandyke.com if they can get me in touch with you.
(Also, to clarify a point of possible confusion: Mosh was developed by MIT students and alumni on their personal time. Think of it as a student project, which has graduated. It started at MIT, but it is not run by MIT.)
Cheers,