When I use my flash bracket, I bolt the flash bracket to the camera. When I use the camera with flash bracket with my tripod, I bolt an Arca Swiss compatible plate to the flash bracket using another 1/4-20 hole in the bracket. A third 1/4-20 hole allows me to leave the $0.75 1/4-20 eyebolt (stainless steel no less) I use for a carabiner + neck strap on the flash bracket.

That said, from an engineering perspective the long term durability of a plastic molded dovetail when clamped in a metal Arca Swiss clamp might be a challenge because the Arca Swiss system is not designed around that degree of dissimilarity of material hardness (not that I have anything against plastic). One of the characteristics of Arca Swiss connections is that they are not based on a formal standard and this leads to minor dimensional variability among components that is mitigated by clamping the clamp tighter or buying components from a company like Arca-Swiss at the prices their products command.

Potential durability aside, a molded in dovetail would increase the bulk of a camera and generally the trend seems to be away from camera bulk all things being equal. While a molded in adapter might increase stability in some cases, in others it would decrease it. Setting a camera on a table is an obvious case. Any other mounting is also going to be through a longer lever arm and with a higher center of gravity.

The QR dovetail would be metal. Most high end cameras have metal shells on the bottom, and that's really what Thom is writing about: high end cameras.

EDIT: and it would not stick out awkwardly on the bottom. It would be engineered as part of the shape of the camera itself, while keeping a flat bottom that sits level, with the 1/4 threaded socket.

I'd prefer dual 1/4 threads on the bottom of the camera, then you could add the Arca Swiss dovetail and it wouldn't have the rotation issues. Also, the aesthetics and feel of the camera body wouldn't change.

A dovetail would change the way a camera feels in-hand. For all the non-Arca-Swiss users, a dovetail would forever be caught on things without adding utility.

It doesn't have to stick out - think two ridges on the underside, but the whole bottom is still flat.

I wish the author had explained this better. It seems obvious now but initially I was having the same confusion as some of the ancestor comments.

Exactly.