I honestly thought this would be easy when I saw the question. I'm not familiar with MW spells so I looked it up first to see if it was a hot, etc. Looks like it works similar to priest Prayer of Mending. That makes it a lot tougher. There are Prayer of Mending trackers that might be able to be modified to work with this if anyone can figure out the code =/
IMO Vuhdo is the best at tracking HOTs because it actually shows the durations really well. Any raid frame replacement like Grid, Vuhdo, or Healbot can track it just fine, and Weak Auras can track the cooldown.
All you need to know is a) who has RM on them and b) whether RM is on CD or not.
I actually use affiniti's wa setup. His renewing mist tracker tracks the number of renewing mists you have and how much time is left on the cast with the lowest duration (for maximizing thunder focus tea usage). Its great, but it still just boils down to "how many renewing mists do I have up".