> Still planned for 3.7: [...]

Eric, please try to get everything you want done and into master as soon as possible, then produce a PR for 3.7, and then we can review it and make a decision if it is appropriate for 3.7.  As I've mentioned in msg310448 and stated elsewhere, the expectation is that the few post-b1 feature freeze extensions granted were only for b2.  Even changes limited to Lib/test can break buildbots and downstream users' testing and take multiple releases to stabilize.  Thanks for your work on this!