Blizzard has indicated that Patch 2.1.2 of Diablo 3 will be arriving shortly after the end of Season 1.
It will actually come 3 weeks before the seasonal rollover, which is itself scheduled on or before February 3. Based on this information, the patch should arrive by this coming Tuesday, January 13. If you may remember, Blizzard expected to put the patch out on December, but of course, that did not go through, so this is long overdue.
Diablo 3 Patch 2.1.2 will be the first one to be released on Windows, PlayStation 4, and Xbox One simultaneously. You can see the details on what Patch 2.1.2 contains here and learn more about how Blizzard decided on the timing of the patch release here.