#1 - Dec. 19, 2018, 2:20 a.m.
Non-Season ERA End: January 8, 2019
Season 16 Start: January 18, 2019
Patch Notes are in the News Blog https://us.diablo3.com/en/blog/22820656/season-16-the-season-of-grandeur-begins-111-12-18-2018
Seems most of the PTR stuff carried over.
-Season 16 Ring of Royal Grandeur buff will be Season Only.
-Cosmetic reward is monarch butterfly wings
-Completing your first GR 70 or higher solo now grants a free Primal AND an Achievement. Makes it easier to verify you unlocked them for that gameplay mode. This is unclear, but it should be per MODE so Non Season HC, Non Season SC, Season HC, Season SC. (Please clarify Blizz if I am wrong).
-Set items should be updated retroactively with the new patch values so you won't need to find them again in Non-Season.
-My guess on patch date is Jan 8th seeing as that is when the Era ends but I could be wrong. The other option would be the 15th but that is less likely.