The PEP is listed as accepted, with you as the BDFL-delegate, but it lacks a link to the public acceptance message (usually on pydev list).

The PR was not rejected by a core dev but was closed without explanation by the author on the same day the last commits were added.  Perhaps OP just gave up getting tests to pass.  But they disappear on closes.  

However, the contribution had been made under the CLA and you or Petr or any other core dev should be able to download it to a local branch, try to whip it into shape, and make a new PR before beta 1, in about a month.  Or start from scratch.

I cannot test downloading at the moment.  Apparently, OP's fork branch has been altered, so that merely reopening is not an option.  The OP used force-pushes rather than update merges, and this often creates problems.