1. M-FM Points System
This could possibly remedy inactivity, as well as add another fun element to M-FMs. This would add a points meter to every person, separate from rep/post count/whatever. The only way to add to these points is by posting in the M-FM board, perhaps with a daily limit (something low like 5 posts/day) to prevent spamming to farm points. Optionally, we can give a certain number of points to hosts as an incentive for more people to get involved with hosting M-FMs. These points can then be used as a general gauge of a person's M-FM activity. We can even have something like entrance fees for M-FMs, tournaments with point prizes for the victors, and betting on the outcome of M-FMs.
I had another idea but I forgot it lol. I'll add it here when I remember it.