Good question.
MM appears to becoming a a standard in some areas of the country. Local, state and even federal teams are now using MM. The more teams who are using MM, the more often the need to share mission data. I know of many, many missions that crossed multiple agencies, but I don't know of any where the larger agency took control of the mission - that's not to say there isn't any, I just don't know of them.
As anyone who follows this forum knows, MM features are driven by your requests and real life issues in the field. It is technically possible to transfer missions between agencies using MM and/or more tightly integrate neighboring agencies team infomation. The biggest concern becomes security, but i think this can be overcome. Anyone who has been a first responder, knows there is are often barriers between agencies working together. It would be great if MM could help break down some of these barriers!
The best thing anyone can do who believes in MM, is help your neighboring, parent, and larger agencies get started with MM. The more agencies using the tool, the more need to share information, and this will drive the ability to do so.
Mike