WordPress 5.3 Development Cycle
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Target date for release of WordPress 5.3 is November 12, 2019 ?
WordPress 5.3 will be the final major release of 2019 and aims to polish current interactions and make the UIs more user friendly. Matt Mullenweg is the Release Lead for 5.3, Francesca Marano is the Release Coordinator, David Baumwald is the Triage PM, Riad Benguella is the Editor Tech Lead, Mark Uraine is the Editor Design Lead, Andrew Ozz is the Core Tech Lead, Anders Norén is the Default Theme Design Lead, Ian Belanger is the Default Theme Wrangler, Justin Ahinon is the Docs Coordinator, JB Audras is the Accessibility Lead, Mike Reid is the Marketing Lead, and Mike Schroder is the Media Focus Lead. All release decisions will ultimately be theirs to make and communicate while gathering input from the community. There will be a new bundled theme included in 5.3.
Note that WordCamp US will be from November 1-3 and the US Thanksgiving holiday is November 28-29. Both tend to involve travel for a number of people and reduced activity; thus the schedule was crafted to allow ~2 weeks buffer from the target release date until Thanksgiving week. Given the effort that goes into a major release, WCUS, and the end-of-year holidays it is safe to assume that activity on core will slow dramatically after the 5.3 release until January 2020; enjoy that downtime and thank you all for your contributions! 
You can view the full planned release schedule on the WordPress 5.3 Make Page.