I've played some more and this is looking really nice, but if you don't mind I have a "small" wish/suggestion for improvement (hopefully).
The size of the green blobs can be varied up to 5 pixels as it is now, I would like to be able to increase that blob size quite a lot, up to 20-30 or even bigger.
The reason being that some motion is picked up easily by the algorithms you are now using, but often there is less obvious motion next to it that is not picked up, unless I increase the sensitivity way up to the point that it picks up details that shouldn't be removed.
Instead I would like to be able to use less sensitivity but a larger portion around the obvious motion is substituted.
Basically be able to get better MC coverage with less sensitivity, so a possibility to get even bigger green blobs would be nice.