Warhammer Underworlds is coming very soon and already we have seen two of the new factions coming in a box set designed to bring new players into the fold. Dreadfane.
The new announcement will be coming July 20th here
https://www.eventbrite.co.uk/e/warhammer-age-of-sigmar-open-day-2019-tickets-62713021335
Additional possible rumors.
via 75hastings69 over on War of Sigmar
https://war-of-sigmar.herokuapp.com/bloggings/3988#comment-4535644271
I did hear some time back there were maybe 10 warbands this season (although I think 2 are from dreadfane as they were SE & NH), the others were (IIRC) DoK, Ogrurrrs (specifically 1 hunter and 1 or 2 animals), Wanderers, FeC (or might have been free peoples I can't remember), Seraphon, Slaanesh, Nurgle and another skaven. I myself would have liked Idoneth but this is a pretty nice mix of stuff, and at least no more Khorne or excessive SE.