While this isn't authoritative, if you go to jira.mariadb.org, you'll see it's targeted to be released at 24 November 2016 (but the galera release claims 13 Oct 2016). This is how I figure out what's coming out next...
On Wednesday, 5 October 2016, <Rhys.Campbell@swisscom.com> wrote:
Hi All,
Do we have any estimation of the release of 10.0.28?
Regards,
Rhys