You do realize that will make the stand larger / bulkier...?
Absolutely no problem with a ~1cm thick stand and a slim screen - and cosmetically speaking it means that most of your cables come neatly out of the back of the stand rather than sprouting in mid-air from the back of the screen. The only downside is that you have to somehow run DisplayPort and power up the pillar and into the screen (which is hardly rocket science).
Seriously, if we're talking aesthetics, look at the Surface Studio (which has that arrangement) and tell me it isn't gorgeous. (Then look at the price vs. tech specs and have a good laugh*).
If we're talking about a replacement for the 21.5" iMac then the electronics aren't going to be any bigger than a 13" Macbook,
without the battery, or a Mac Mini with a much reduced (possibly even passive) heatsink. The existing iMac was designed to hold spinning rust, a discrete GPU and hot, sweaty i7, so it's going to get slimmer whether the guts are in the display or the stand.
You think the "design and form factor" of an all-in-one desktop computer that has traditionally had a 27" screen, is going to "basically be a big iPad".
Given that the existing iMac looks like a giant iPad 2 on a stand (albeit with added chin) and hasn't been updated since the iPad 2 was the new shiny, it's a fairly safe bet that the new iMac will
look like a giant 2020 iPad Pro on a stand.
...and while it's pretty much an established fact that it's going to be running Mac OS and not iOS, it's also an established fact that it's going to be capable of running
iOS Apps some of which have been designed from the ground up to use touch and stylus input and would be much more usable on some type of 2-in-1 or convertible. Apple will keep saying the Mac doesn't need a touch screen up until the day that they make a Mac with a touch screen - something which is now pretty much standard on PC laptops/all-in-ones as soon as you opt for a 4k/Retina-class display.
So what are the other characteristics of "a big iPad" - Limited i/o? Apple do so love cutting out ports. Non-expandable? Nobody will be surprised if the new iMac has soldered-in RAM. So I don't really know what the argument is about.
Also, remember, there are effectively
four different iMacs to replace - the 21.5" non-retina, the 21.5" 4k, the 27" 5k and the iMac Pro. It's unlikely that there will be 4 different replacements, but neither is one size going to fit all. It's conceivable that we'll see one iMac to replace the 5k and the Pro - possibly using the rumoured second generation Apple Silicon - and another to replace the 21.5" non-retina and 4k. Since the 27" got a spec bump this summer and the 21.5" didn't, that adds to the plausibility that the first iMac will be a low-end model replacing the 21.5" and we'll have to wait for the second-gen ASi for the 5k replacement.
Apple Silicon is a potential opportunity for Apple to re-arrange their Mac product line, so I wouldn't assume that everything is going to be a 1:1 replacement for an existing Intel model. For starters, with all the i3/i5/i7/i9/Xeon nonsense swept away we could see a simpler CPU choice of "Apple Silicon" vs "Apple Silicon Pro" (whether or not they use those names, and regardless of whether they are physically different chips or just distinguished by "binning") separating the Macs from the Pros.
