Is Tevinter in DA4 even confirmed?

It was heavily implied by the end of Trespasser:

Inquisitor: "Then we'll find people he doesn't know"
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But no, I don't believe it has been confirmed by the developers. 

It is confirmed.

In my heart.

It's about as confirmed as the devs could possibly make it without explicitly saying "hey, we're going to Tevinter!"

"A shitty place full of angst ridden shitty people" is highly subjective, not to mention that everywhere we have been thus far has had such themes, not just Kirkwall and (soon) Tevinter. We have already seen depressing, morose visuals and oppressive, terrible people in Ferelden, Orzammar and Orlais as well, and there were still occasionally moments of hope, namely in Ferelden and Orzammar. A positive you might be able to take from it, is that the protagonist (along with Dorian and Mae) might just get the opportunity to improve upon Tevinter's awful customs like slavery and class system, which in turn, will likely improve elsewhere as well
I'm more worried how they will approach these topics and themes. Dorian's conversation about slavery definitely still makes me glare at my screen.

Ye gods, it better be. Nothing else really for me to look forward to.

I don't care where the game takes place as long as they get it revealed and released. Not to mention we have that Inquisition and Solas issue that needs to be resolved, not pushed under some table mission.

With the Eluvians, we could be anywhere.

Sorry, no. Dragon Age was always a dark and adult franchise, and you knew it coming in. You can't go to a traditional Chinese restaurant and complain that they have no pizza .

Evil people don't really do angst, most of the time. They don't think they're doing anything wrong, so what is there to be upset about?

And as far as the good people of Tevinter, the Lucerni faction is on the rise, so that seems pretty hopeful.

Besides that, Tevinter has plenty cultural beats unrelated to evil magister stuff. Their art and architecture are supposed to be pretty spectacular. According to Dorian, they're relatively free with their emotions. The underclasses would have their own interesting societies that we currently know nothing about. Due to proximity, there'd also be the interplay with dwarven merchants, and peeks into the less military aspects of Qunari culture.

We have a shitty impression of everyone from the north, because most of the people who'd have reason to travel to the south would be soldiers, spies, or slavers. But these societies also have farmers and weavers and bakers, just like everyone else. The evil empire portion of their society must (by necessity) be relatively tiny - soldiers and villainous nobles don't put food on the table.

Nevarra, as long as the voice actors can do the Cassandra accent, Free Marches done properly and Rivain. I'd say Antiva, but I'd suspect they'd lay on 'edgy' Crows far too much.

Dark and adult is fine. But to be dark you need light to compare it against. And angst and acting shitty is not dark or adult, it's teenage petulance.