If I was going to send messages to a Mycroft remotely, I’d be tempted to set it up to do it over IRC or the like. Could even have multiple Mycroft units (and possibly other types of devices as well?) “talk” to each other that way.
Heck, IRC used to be the preferred way to run a botnet, and while custom web services have apparently taken over as the most popular way nowadays, almost as many are still using the old tried-and-true IRC approach instead of the “new” approach.
I know, a handfull of Mycroft units and whatever other devices may be talking to them is different than a botnet, but I still think that having them communicating with each other that way could be a handy trick to “borrow” from botnets still.