I was also unable to buy a Vision Pro due to the prism restriction, and your comment about how prevalent the potential need for prism correction is is useful, as it was hard to find any statistics for the US. I only knew anecdotally that both myself and my significant other have a small amount of prism correction, and some strip-mall shops don't have the gear to test for the need (although some do).
Ironically, the only place I did find any hard numbers was the info pop-up on the Zeiss page that lets you check whether your prescription can be made as optical inserts. That info says "less than 5%" of eyeglasses made in the US. Which, assuming that "less than" means somewhere between 4.1% and 4.9%, means it's rather disingenuous to call it "rare"; roughly 1 out of 25 glasses-wearers (and therefore roughly 1 out of 40 of all US adults) is certainly uncommon, but it's rather a stretch to call it "rare" (which in my mind is <1%).
Also ironic that the help page outlines that there are Accessibility features for people with more uncommon binocular vision problems (lazy eye, drooping eye, or even just one eye), allowing them to use the headset either with their hands or by tracking just one eye of their choice. You just can't get prescription inserts with prism (or very strong prescriptions for severe myopia or astigmatism).
Personally, I just wish that Apple had mentioned it (or made that Zeiss page available) prior to the pre-order, so I didn't have to get up at 5am only to realize I was unable to use it.
Now that a little more info, and some reviews, is available, it does seem like this is not an unaddressable problem. Since the eye tracking is inside the lenses, and is calibrated prior to use, that end of things should just be able to adjust to wherever your eyes are pointing as long as it's consistent (and worst case you could get all of the prism offset in one lens and set it to only track your other eye). One review did mention that when Vision OS didn't have the correct prescription set it wasn't noticeable but did result in slight nausea during use, so presumably the OS is adjusting what's on the screens for the prescription in some way; that software integration may be why prism isn't supported. It's also possible that Zeiss isn't bothering with less common lens designs since Apple is already selling more headsets than they can manufacture anyway.