The teaser is, quite literally, a tease.
It continues the story from the end of Trespasser (which was expected), features the Dread Wolf himself (no surprise), and is supposed to be releasing not any time soon (excuse me while I sob quietly in a corner).
We can assume a few things, though. The game will take place in Tevinter, since Trespasser ended rather unsubtly with a knife stuck in a map. It will probably not feature the Inquisitor, since Bioware has been steadily retiring the protagonists of each instalment of the series (i.e., the Warden and Hawke).
Personally, I’d love for the Inquisitor to the protagonist, especially after having lost their arm at the end of Trespasser – it’ll be intriguing to see how Bioware would make something like that work when so much of the Dragon Age experience involves combat.
I think it’s also safe to presume that some familiar companions will return – Varric; perhaps Morrigan; Leliana, Cassandra, and more if Dragon Age 4 is about the Inquisitor; probably Dorian because, y’know, Tevinter; along with a smattering of others.
But at this point, it’s all speculation and guesswork on my part. With any luck, we’ll have more news soon but with the game 3 years (or more) away, I highly doubt it.