Yes, it does rewrite and map back subscriptions to users.
So does this then recycle duplicate subscriptions? The diagram on the home page seems to suggest so, which would be much more efficient, though I'm not sure how often that would actually happen. Also, in case you weren't aware of it, I have a similar project: https://github.com/coracle-social/multiplextr
Discussion
Cool! I'll have to look more closely at the source.