I apologize if this question warrants a beating with the search engine button, but has there been any fan project in making rules for a weasel campaign? Seeing as they’re one of the few sentient species out there (apart from their species cousins, and apparently bats and owls, according to the Winter comics) it’d seem interesting to play the bad guys and all their crazy Darkheather burrow-stealing intrigue.
Or maybe the ferrets making their scheme for an uprising against their oppressors - the weasels? What to do with ferrets playing along with the weasel? Can ferrets make deals with mice? Do ferrets and mice has interests in common, what happens when the uprising is over? Or am I just a little obsessed with ferrets? 
Well, if your signature, avatar, and member title are of any indication… 
(‘‘illern’’ actually means ‘‘the ferret’’ in swedish) There will be ferret uprising in my hack SPQM
I think your idea would be interesting, especially if one could ‘‘twist the view’’ so the weasels no longer obviously are the bad guys.
I love the description of Weasel Nature on page 203:
“Their Nature does not encourage them to hide & flee. Instead, it drives them to trick their prey, kill them, take their stuff & gloat about it.”
Sounds like another game would fit just perfectly for a weasel campaign. Mouse Guard, however, is about fighting for what you believe, despite the danger. Not about killing things & taking their stuff.
But, to be fair, in the last demo game I ran for some pre-teen kids their mouse characters were tying up & torturing captured weasel scouts; so maybe the weasels might have their own version of how things really are in the Territories.