My opinion:
Chin - Yes
Notch - No
Price - $1999-2199 with an 8/14 M1 Pro, 16GB of RAM and a 512GB SSD.
The Price seems doubtful. The current $1,799 iMac 27" model currently has:
i5, 8GB RAM , 256GB SSD , Radeon Pro 5300 4GB VRAM .
So boosting up 8GB of RAM and 256GB of SSD in costs. ( Apple really hasn't changed their RAM and SSD $/GB pricing. with M1 versus Intel). There is a bit of cost savings in dumping the dGPU and VRAM. Possibly could just swap most of those costs increase/decrease. However, haven't even touched going from mature 5K IPS display to. mini-LED. The MacBook Pro 13" to MacBook Pro 14" jump was about $200 for a one inch larger new tech screen. This 27" screen has a 90+% bigger diagonal. ( it is going to be more expensive to make ). Kind of dubious paying for that with just some relatively low end dGPU ( cheaper than what was in the MBP 16" intel model) and some rather limited amount of VRAM.
The current model iMac 27" has a. "standard glass" and nano-textured glass ( +$300) options. I would not be surprised at all if the entry level iMac was $1,999 ( $1,799 + $200 ) , but with the 5K IPS screen. It would get the same RAM and SSD minimal bumps that the MBP 14" got the screen is left there so they can technically limbo dance just under $2K. The rumors wouldn't be talking about the "boring" display entry model because not "sexy clickbait" content. ( Apple might technically need a new IPS panel because the bezels are thinner but it wouldn't have the manufacturing growing pains that the mini-LED is having. )
Instead of having a "nano-textured glass" option, Apple could just have an mini-LED option. For the large volume entry iMacs that gets them around the volume limits on 27" mini-LED screens. For the "upper half" configuration iMacs, a $300-500 mark up on screen gets Apple higher margins. Apple possibly could have an even higher mark up on nano-textured miniLED models ( which when coupled to 32-64GB of RAM and > 2TB of SSD would be pusing close to the intel iMac Pro prices. ). However, I would expect Apple to wait for 2nd gen mini-LED production before weaving in nano-glass to the process. Something to do in 2023 if M2 Pro/Max are relatively more modest bump upgrade.
Same chassis/product line with two ( or three) variations on the display panel. Apple could trickle the "Pro" suffix down to a 27" model with an M1 Pro in it. Part of the issue is that the current Intel 27" models have a pretty broad range of CPU+GPU combos to choose from in configuration. Limiting to just an M1 Pro + M1 Max is going to be more limited to what they have now. Apple can compensate by adding display options.
If they didn't cripple the chassis thermally possibly could get a "M1 Max Duo" in there and solidly have configurations in the old Intel iMac Pro price range. However, tossing the Ethernet into the power brick is a bad sign on that front.
As for notch / chin ... no notch likely means at least as much a chin so that top/bottom are symmetric. "Stuff the major electronics into the chin so can make iPad thin" , that seems doubtful given the thermals a. M1 Max needs to cover and its package size.
Notch is primarily to incrementally stretch to get some more diagonal space while limiting the height growth. The 27" iMac stands vertically.... there is no pressing limitation to match the height of the iMac to the depth of the keyboard+trackpad. It would be just more expensive to make/produce for no material gain in function. jumping from 16 -> 27 in screen size , they are already
past trying to incrementally bigger screen area. They have a bigger screen.
I think Apple is sticking to 27" because it helps control the costs ( don't want the entry iMac price to raise too far because it will drop too many buyers who want something better/bigger than a 24" screen. ) . But also gives them an option of controlling costs even more by not bumping the screen tech.
If Apple does a Mini with the M1 Max, then the folks that "have to have" a 32" screen have a "Mini + XDR" path right there in the product line-up . Apple doesn't have to make the iMac cover that. Especially, if they are capping the iMac SoC usage to the same boundary as the upper-end Mini. Need a bigger screen.... buy one. ( it won't be like you are loosing performance )