Also, just supporting some basic features, like shutter and all the exposure settings, shouldn't be that hard... I bet all of these are already implemented, because many cameras have smartphone applications that do allow to control all of these.
Thus, the largest cost would be mostly documentation, packaging and support for the various OS. Which, although might end up being quite a non trivial amount, it could be seen as money well invested in brand building, especially since now, in 2022, only professionals or invested amateurs are buying these dedicated cameras...
Right. Engineers usually underestimate how much this really is. Often by an order of magnitude or two.
I'm pretty confident their margins aren't fat enough they'd be happy considering eating 1-2% (i.e. your numbers) on something that might help a fraction of install base. Hell they may already not be making next to nothing on these bodies.
So it would be a real project, and it would cost them enough that (using your rough numbers) they'd need to sell probably a few thousand support contracts a year to justify doing it properly (supporting multiple cameras, customer support, testing etc.). So I imagine if they have looked at it, they've balanced that against the "brand building" as you put it, and aren't sure it's a net win.
The prosumer space is funny for stuff like this, as people are often quite capable but not really willing to pay enough to justify the cost of real support. Some companies solve this by throwing something unsupported/unofficial over the wall, others (or their lawyers) decide the whole thing isn't worth the hassle.
I've got the cash for a great canon camera. I used to carry one around with me all the time. The size isn't what's stopping me. It's the UX.
Camera makers (even camera divisions in more "high-tech" companies like Sony) are very much traditional hardware-first companies, I'm fairly certain he idea of opening up the cameras is just alien to them.
How much are you willing to pay for this? I suspect they've all looked at it, and decided the ROI wasn't worth it.