Thanks! I read the document earlier in the day and I think it is a truly excellent document -- it ramps up slowly enough in term of sophistication, so that people that already know a bit about GC stuff but don't routinely work with them can refresh their memories on the fly, and it goes into far more details than what I have previously seen (except an in-person talk by Stephen a couple years ago, but many things seem to have changed since then.).
One thing that I did not realize about your design before is the very subtle interaction between the fiber switching machinery and the GC. This aspect is fairly complex and easy to not think of when reading a description of the GC in "normal" functioning (without fiber switches), or when reading descriptions of the user-side of fiber scheduling (ML programming with effects, where it is natural to forget about GC interaction).