I don’t think that’s the goal. The 24 already exists.
For history of iMac Apple hasn't really separated the product baseline design by screen size. The larger screen one was just a proportionally larger version of the smaller screen.
Even the iMac Pro was stuffed into the same dimensions as the "regular" iMac ( with some minor , largely visibly hidden, adjustment to push more air flow throw the system. bigger vents that consumed "ram door" )
This presumption that they are no going to put the iMac 24" on radically different path than iMac 27" would be a leap. Perhaps "iMac Pro" is suppose to decouple the two products.
Tallness is irrelevant for an iMac; depth is the constraint that currently makes anything like HDMI impractical. (You said this yourself for SD, so I’m not sure why you bring up height here.)
HDMI Type C socket is entirely practical. Even on the back of the thinned out iMac ( no bigger a depth constraint that type C USB. )
I also said there was a very simple solution to the SD card if keep the 24" like thin profile; just put it on the side. Same solution as the headphone jack ( which has just as awkward depth problem. ).
Ethernet won't fit if rotate the socket 90 degrees and put the socket on the side. It is "tall". ( rotated 90 degrees it would be to "wide" ; same issue just rotated 90 degrees ). Largely the same reason it got tossed from the MBP when Apple shrank the height. Rotate the bottom base of the headless MBP 90 to vertical , the issue doesn't go away.
The "short"/"tin" ports with depth can be simply put on the side. Even easier on a much bigger screen where the main logic board can be more centered in the middle farther from the edges. The SD card slot is "short"/"thin" so if rotate it 90 degrees on the side so vertical depth won't be problem.
Since Apple has to build power bricks with ethernet for the 24" model, they may push for economies of scale to push that kluge onto the iMac Pro too. That would be dubious for an upscale desktop, but if on a "magically thin" kick (and still trying to hide the ventilation to make it more "magical" ) it is a move they have a track record of following.
P.S. I'm not saying Apple should do it. Put they can if they want. HDMI has multiple sockets to choose from. And SD card is same problem class as the headphone jack.