To me, the degree to which a camera is likely to see a built in Arca Swiss plate is inversely proportional to the degree to which it costs multiple thousands of dollars because the higher the price the more modular the design. The reason for more modular designs is that the variety of systems with which high end cameras are designed to integrate tends to be higher. Or conversely the more likely the camera is to be designed to lock the photographer into a proprietary systems sold by the camera manufacturer.

In terms of adding a second screw, a multiple thousand dollar camera body is probably not the ideal first subject for a person who has never disassembled a camera or done similarly fine grained work. Such a person should perhaps hire a technician or practice on broken equipment first in cases where such modifications seem worth the effort/cost. Hoping camera manufacturers would design around the edge case is not much of a plan.

I think the inverse proportionality is probably wrong since entry-level cameras generally never get mounted on anything. Arca Swiss mounting on my mom's camera wouldn't be particularly useful.

I don't think a multiple-thousand dollar camera body is a good target for invasive modifications unless it's already out of warranty, regardless of whether the change is being made by someone with the appropriate skills. I also doubt that the result of such a modification would be very good anyway. Without being part of the initial design (e.g. a captive nut embedded in the base), the best aftermarket modification would likely be based on either threads tapped directly into the body or a nut essentially glued in place.