Excellent work on the rewrite. To summarize for those that do not have time to read the whole document, it's the same spec, it's just been rewritten to read more clearly. I think it's a great improvement over the previous version.
I have two suggestions:
Section 4, "Tor Configuration", I think should be moved into another document and a reference should be added instead. While it's useful for developers reading the PT spec to see how to configure their Tor nodes so they can test their PTs, this information is going to be used mostly by bridge operators. Bridge operators shouldn't have to go to the PT spec to figure out how to configure their bridge. PT developers though will need to configure a bridge anyway, so I think it's sensible to at the end of the PT spec send them to the bridge configuration documentation and the PT configuration section specifically.
Section 6 "Future Improvements" I think should be moved into a PT roadmap document. There is a lot to discuss regarding future improvements. My list for the most part does not overlap with this list. We could engage in healthy debate over what should go in the future improvements section, but this seems to me to be something better done when drafting a roadmap document rather than in the spec. It would of course be useful to add a reference to any roadmap documentation at the end of the spec.