WordPress 5.3 is planned to be released on Tuesday 12 November 2019 with a Beta 1 on Monday 23 September 2019.
Given the large amount of accessibility tickets in the milestone (75+ Trac tickets, with 57 still open tickets as of today), two additional accessibility bug scrubs are planned:
These bug scrubs will be specifically focused on technical issues with current Trac tickets.
Regular weekly bug scrubs are still planned each Friday at 14:00 UTC.