Baldur's Gate: Descent Into Avernus is going to be the Prequel to BG 3. It's going to have an updated Gazetter for Baldur's Gate, kind of like how Waterdeep: Dragon Heist got Volo's En****** to Waterdeep as a Chapter in it.

I'm hoping it has a more in-depth look at the newer districts then Murder in Buldar's Gate did.

I'm looking forward to it. It's also supposed to have a mechanic that found it's way into Baldur's Gate 3, but we don't know if it's infernal deals or Infernal Warmachimes or both or something else.

I wasn't going to buy BG: DIA, I was tired of Swordcoast APs, but BG 3 changed my mind, and I pre-ordered it off of Amazon.

Here is some stuff to read and download.

http://www.dragonmag.com/5.0/#!/article/117400/103786214

Here are some Videos to watch.

More info on Avernus, from developers Chris Perkins and Adam Lee:

warmachiens sound lke a stretch, but itd certainly fit Larian..

They might struggle to justify bringing them out of the Nine Hells, especially as they are literally fueled by the souls of the damned.

It won't matter that it doesn't make any sense. As long as Larian promises WotC lots of income WotC will agree to anything Larian wants to do no matter how ridiculous it is or how much it violates long-established FR lore.

It would be cool to find known damned souls in the Avernum hell, like Irenicus or Safana.

I think them adding in Infernal Deals machanic is more likely then Infernal War Machines.

If you are not planning on buying this product and are a little curious about this campaign´s story, they are making a miniseries here on IGN
https://www.youtube.com/watch?v=cxk8bM5OBEw

You can learn a little about Avernus and watch an infernal machine fueled by damned souls in all his glory.