There has been no indication of a new campaign setting.
If we were to try and divine when a new one would possibly get released... we need to extrapolate WotC's publishing pattern going forward. Thus far, their non-adventure book has appeared once a year in the autumn:
Sword Coast Adventure's Guide, 2015 (setting gazetteer, some character stuff)
Volo's Guide To Monsters, 2016 (monster book, some character stuff)
Xanathar's Guide To Everything, 2017 (character stuff, some DM stuff)
So then we wonder what logically comes next? For many of us... we're guessing that 2018 will be a 'Manual of the Planes' type of book, along with additional character options. Whether it's strictly inner/outer planes info, or if it also includes alternate Material planes (IE other settings) is up in the air.
So a completely new settings probably won't be illustrated then. The closest we might get would be if they were to create gazetteers or chapters in the book of the various known settings and include one that is less-known to many people, especially players from the last couple editions (Mystara or Birthright for example).
For 2019? Well, if they decided NOT to includes other campaign setting info as part of their 2018 planeswalker manual, then THIS is the year we'd most likely see something. This book would include larger sections of info on all the main other settings, and actually would be more likely to include a completely new "small area" setting like the Nentir Vale was for the 4E books. It wouldn't be a full world (because you wouldn't be able to fit enough detail to show off an entire new world into what would be a single chapter in a settings book) but a small duchy might be doable if that's what they chose to do.
After 2019? At that point who knows... we would have past the 5th year of the edition's life cycle, so at that point your guess is as good as mine what they might produce going forward. The one thing I *do* believe though is that they WON'T produce a single "campaign setting" book-- new or otherwise. I just don't see them putting in the time, energy, and money for the design, development, art, cartography, printing, etc. for a book that only a small section of the player base would actually want. Especially when there are any number of other companies out there that have been willing, are willing, and could be willing to pick up the slack to produce new campaign setting books. Green Ronin has already done that with the Tal'Dorei Campaign Setting, and other companies have joined in. So there's really no need for WotC to do it as well.