Fourth follow-up to the OP:
Today I test-drove a base Cayenne "4" Coupe at Porsche Stratham (NH). Things were pretty much as with the regular Cayenne "4", with the exception of: (a) no dual sun visors for the front seats (i.e., only single sun visors); (b) the mirror view out the back window was surprisingly good with the slanted back (which makes for much less cargo space, of course); (c) there's a pano glass roof with no way to open it and no closing sun shield; (d) rear seats are manual, not electric, to put the backs up and down (a plus over the non-Coupe seats, for inexplicable reasons). There are two rear cargo-area latches to release the back seats (1/3 left side; with the right 1/3 and center as the second one), and they just fall down, suggesting it's just a mechanical release.
Regarding the view out the rear window, with the back headrests down as far as they'll go, the intrusion into the back window was much less than in the non-Coupe Cayenne Electric; I was expected worse, not better with the Coupe. I learned a few things also today: to set the ACC, you have to push the button at the end of the stalk, and then it shows you a menu, and you keep pushing that same button to toggle through to get ACC (this is unlike any Porsche I've ever driven before). I also had significant problems (again) pushing/touching the square on the charge-port doors to get them to open; I finally got the NACS port door to open by pressing for a few seconds, but never got the J1772 port door to open. I realized today that there's an icon in the upper left corner of the big infotainment screen that's always there when the car is in Park, and touching it gives a screen that allows you to open the frunk, rear hatch, and both charge-port doors (and you can close the charge-port doors that way, also) -- so that's definitely how I'll always be opening the charge-port doors (i.e., not from the outside, as I'm used to doing with my Taycan); too bad that Porsche messed this up.
The exterior of the Electric Couple looked better than I expected. But I still think that the regular Cayenne Electric looks better on the exterior. When the headlights are on in the daytime, the rear light bar lights up noticeably even in sunlight, as well as the PORSCHE lettering on the rear; this Coupe was optioned with the black rear PORSCHE lettering -- so it appears black when the headlights are off but red when the headlights are on. Unfortunately, this seems to be the case when ordering the Glacier Blue rear lettering also (i.e., blue with headlights off, red with headlights on). I wish that Porsche would give us the option to not have red PORSCHE lettering. Also, I don't see a rear glass wiper on the Coupe in my photos (I didn't notice this when I was with the car); it doesn't seem to be even an option in the configurator, whereas a rear wiper is standard in the regular Cayenne Electric. Lots of curious design choices here that differ in the non-Coupe vs. the Coupe -- more than just the sloped back (which also has the moving spoiler below the window in the Coupe, vs. it being located atop the rear window in the regular Cayenne). The color of the exterior of the Couple that I saw today is "Chromite Black Metallic". With $4410 USD leather interior in black/Magnesium Grey, $2910 Augmented Reality Head-Up Display (which I forget to try out in detail, though I noticed good navigation instructions projected onto the windshield above the steering wheel), $1320 21-inch RS Spyder Design Wheels, and $7290 Premium Package, the MSRP on this car is $137k USD.
Everytime I use that new curved touchscreen in these Cayennes, the more impressed I am with the design. I cannot think of a better cockpit in any 2026 model vehicle on the planet than this one.
[addition 2026 Sept. 13, so fifth follow-up to OP] I test-drove a Cayenne 4S Coupe at Porsche Nashua (NH) yesterday. Nothing really to add except that I confirm my previous comments about acceleration: it really seems lethargic compared to my '21 Taycan 4 CT, and to the point that I don't really see that it's all that much faster in accelerating than the base Cayenne "4"... I was able to take it on some curvy roads, and I was impressed at how planted it was taking curves at fairly high speeds for such a whale of a vehicle (this particular car had rear-wheel steer also). I drove my Taycan to the test-drive and home again afterwards, and was comparing the acceleration from stop (at a traffic light), and the Cayenne 4 and 4S (and Macan 4) are all much much worse (more lethargic, slower to accelerate).
Other things I picked up on the Couple differences from the normal Cayenne boxy version: rear seat center headrest goes way down below rear-window in the Coupe, which contrasts with the regular Cayenne where the center headrest blocks a fair amount of the rear window; strange... Pano glass doesn't open in Coupe, and I think it's standard in Coupe, and there's no mechanical/electric sunshade to close off sunlight. Dual sun visors are missing from two front seats (they are standard in non-Coupe versions); this again is very odd. Also, this launch car had only been test-drive once before, I think (it had 24 miles on the odometer), and the predicted range was quite low even after my spirited driving over a half hour where I got it up to 90 mph on expressway and did curvy 2-lane roads (predicted projected range only 272 miles on a full charge; I do realize that hundreds of miles need to be driven to calibrate this properly, but that's still quite a bit lower than I'd expect in the first hundred miles of a new Cayenne electric).
I have a base Coupe. I think the variable light roof is necessary - as you say there is no blind. Once ACC is selected then it becomes the default and Voice Control is easier to use to change it whilst driving.
I’ve read on here that the SUV roof spoiler doesn’t deploy until 70mph - if thats true then here in the UK police wouldn’t need to use any speed cameras or guns to prove you were speeding. Only joking because I’m sure you can manually deploy it. On the Coupe it deploys at a much lower speed, in Sport Plus you see it fully deployed in the rear mirror so it dies intrude a bit into the rear view.
As you say, the rear wiper is not an option on the Coupe. I had the glass treated and the lack of a wiper isn’t an issue. That said, we have had very little rain in the UK since I bought the car. I didn’t have a wiper on the Macan and that wasn’t an issue either.
The rear seats are 1 way electric - only the backrest and It doesn’t recline very much, I think it’s really there so you can make them upright to increase the rear luggage volume rather than for comfort. I personally wouldn’t like to sit in the rear with the backrest almost verticke. I‘ve seen complaints about the SUV’s electric lowering and raising being a bit of a pain due to being very slow.
I initially had a problem opening the charger doors but now have the knack - I followed the video. Opening the doors from outside you have to have the cable ready to plug in as the door closes quite quickly. If the door closes as quickly opening it from the dash then I couldn’t get out and plugged-in in time, so I’m sure it doesn’t have the same restriction.
I went with the 21” Spyder wheels and the car looks much more like a Porsche than the standard 20” Aero wheels (to me looks like they’ve come off a Nissan Leaf !).
The reduction in rear luggage size wasn’t an issue for me as it’s the same volume as the Macan EV which I never found too small.