Very interesting. It's a shame the image is so pixelated, so we can't read what the blue thing is. I wonder who the new person is (the one next to Sentafruice). I can tell he's a descender, because he's wearing the scarf. The fungus is interesting, because it means that's probably what was used for light, since it glows. On a completely unrelated note, I loved your 10 year image, it looked just like a Chris Riddel image! :)
I have good news and bad news. Good news: Apparently the before now unrevealed Descenders hardback cover is revealed! I have tried to attach it to this post, but if it doesn't work then you can see it on amazon or penguin. It looks awesome, but I don't think that it reveals anything new. Bad news: The Descenders may not be coming out as soon as we thought. Both amazon and penguin say it is to be released March 7, 2019, and Goodreads says September 20, 2018. I don't see a source that says July 2018 anymore.
So we now also know that there will be a banderbear (probably Weelum) and I've thought that the other descender might be Slip. I also like the look of the creature from under the Edge, although that doesn't look like a flying one.
I think I've got a better image.
It's also interesting that this particular hardcover is an old-style one, with lots of characters. I wonder what they will do with Doombringer, since Paul Stewart said they were considering a Doombringer hardback. If they made the Doombringer one similar to this, then The Nameless One would be the only one without an old-style harback, I think.
Sorry DDB, but I have looked around some more and haven't found anything with a sooner date than what I said. It looks like they are in fact doing this to us. :( Thanks for getting a better quality image. On second thought, I think that the cover does have a few relevant details. If you look at the phraxcraft, it has a little jet of phraxfire coming out of it, which seems to confirm the idea that the phraxchamber supplies propulsion while the wood gives lift. Also, the weird creature in the top right looks similar to an Edge wraith but it isn't, which seems to confirm that there are other lifeforms down below the Edge. If Celestia is on the official cover in descent equipment, then I think that we can be sure that she is going on the expedition (no guarantees that she lives though)
Everywhere (Amazon, Penguin Book etc) I looked it has the 9th of March, 2019. That's still over a year away! Maybe there were some issues we don't know about. The original publishing date was supposed to even be in 2017, wasn't it? The Edge Chronicles Facebook (as always) hasn't done the cover reveal yet, but they were also late the last time. Anyway, having a complete cover is a good thing. And I am very sure Chris a Riddell will post some more images over the course of the next year and then we'll have more to speculate about.
Having read WNW, I now have a couple more things which I think I can add to this conversation. I think that Forden and Gart's journey to to the Eastern Woods in WNW will be very similar to the journey to The Edge in The Descenders. We know the Midwood Decks (and therefore the who Midwood area) will be making a significant appearance in TD, so it's likely that that's where the tallow hats will appear, just like in WNW. I now know that the tallow hats were the slavers who lived in the floating fortress, so that's probably where they will appear as well. Since they'll have to pass over the Twilight Woods to reach The Edge, it's possible that they might buy some illicit stormphrax from a mine, just like in WNW. I think it's unlikely that Celestia will die, because Alcestia dies in the "Doombringer" part of WNW.