It looks like some fresh news has come out since I last posted about Dragon 4. For starters, there was the teaser trailer released in December of 2018, which gave DA 4 a working title of The Dread Wolf Rises.
There isn’t too much info here, but it does confirm that Solas (the titular Dread Wolf) will play an important role in the game.
Btw, if you want a quick summary about Solas/the Dread Wolf, this humorous Reddit post is a great explanation of why he’s such an important character in the Dragon Age universe.
Coupled with the ending of DA’s Trespasser expansion, the most likely guess is that the story will involve Solas (the villain?) trying to destroy the Veil to merge the normal world with the Fade.
Since that’s pretty terrible for everyone in Thedas, the protagonist will presumably try to stop him.
As for the release date, according to EA’s recent earnings call, DA4 will not be released at least until 2022.