We can guess they might also be revealing if we're going to get any non-adventure supplemental material this year as well, as the Stream of Many Eyes was where Xanathar's was announced. I suspect that while it may not be spelljammer, we're absolutely going to a new setting for this next one (for real this time guys, I promise!) I wouldn't be surprised to see Dark Sun given that they've had psionics in the works for a hot minute by this point. I also expect that we'll see some combination of the september and november release be devoted to a combination of a new adventure and source book for the place the adventure takes place in.
Given the Descent title, it almost makes it sound like another dungeon crawl, but we just got mad mage- and we've already done the descent into madness motif, I'm about ready to call it as a planescape esque adventure taking us to the nine hells, especially looking at that illustration of an angel descending toward demonic hands. This is suggestive that it would be planescape, rather than Dark Sun, which would make a lot of sense with the hints that they've been dropping.
The art style reminds me of a few Magic angels, but none of them quite fit. The only MtG Angels with 4 wings that are blind are from Zendikar. But they are very specifically blinded by their own Halo's, not cloth.
8 devil hands reaching out for an angel? And Chris Perkins and Greg Tito just did a lore you should know about the Nine Hells and talked a lot about Zariel, who also got a stat block in Tome of Foes? I'm thinking a Blood War story with a Zariel showdown is incoming!