I haven't read through all the replies in this thread, so forgive me if this has already been brought up but I have a couple of points I'd like to make.
As to the window on the rear, IIRC the reason they went that way, was to help with radio transmission. That started with the Nexus 6p. While a completely metal back would look nicer (although that's a matter of preference) I'd take better performing radio transmission any day, especially as someone who lives in an area with low signal levels.
As for them using an LCD for the screens, while I'm sure these newer LCDs are better than past iterations, they're inherent properties run in contrast to some of the goals they're trying to achieve with these devices.
First, LCDs aren't going to be as efficient for something like Always on Display. OLED displays work better in that they only turn on the pixels necessary to display the pertinent information. With an LCD, the entire display has to be turned on, so it won't be as efficient as an OLED panel.
Second, if the new panels aren't compliant with Daydream, that's another mark against it. Third, while recent LCDs have gotten better in terms of contrast, they still don't match OLED panels. And how are off axis viewing angles, as those used to be horrible with LCD panels.
While I understand wanting a larger display, at some point it stops being useful for one handed operation, which was the point of the smaller Pixel model. So if they can increase the size of the display without increasing the physical dimesmions of the phone, that's probably ok. While I dont like the elongated displays pioneered by Samsung (it's fine for watching video shot in that format, but for everything else like 4:3 & 16:9 video and images, it's worse). But since that's the way the industry seems to be moving to, there's not much I can do about it.
Some have mentioned using the display/glass to transmit sound instead of traditional speakers. While it would allow bezelless phones, I can't help but think that volume and clarity will take a hit.
I hope they do go back to the flat glass instead of this 2.5D stuff they've been using. For one thing, if you use a case and screen protector, it doesn't work. The whole glass protectors won't work with cases, and the ones that cover just the face don't last. My SP on my Pixel 2 has 2 spots (the top corners of the phone) that have lifted after a month to 2 months. This happened with the previous 2 SPs I installed. Apparently the only option is either the film protectors that don't feel like glass, or this new brush on coating that's recently come out. Since that's new, it's longevity can't be spoken to.
From what I also understand, the new devices will be covered in glass to allow for wireless charging. I should've known this would happen when Apple introduced this on their line. Now the need for a case will be even more necessary. I used wireless charging for about a month a few years back, and found it more cumbersome than just plugging in the phone. It's not as fast, it causes more heat generation (simply from the induction process) and placement was a pain. So to add a fragile shell to the device to accomplish this, it's benefits are outweighed by the potential risks IMHO.
So that's the end of my rant. Depending on the final product, it may be time for me again to go to another OEM. While I like the GA integration, fast updates, and minimal skin compared to AOSP, I'm worried they're just going to incorporate a hodgepodge of features from other OEMs to compete rather than setting themselves apart. The problem seems to be that all the OEMs are doing the same.