It would be incredibly expensive. Nintendo gets the parts for joycons, at the price they do, because they are making millions. A third party would be producing 10k at best, and that would be a gamble, even for someone like Nyko. They would get no where near the discount Nintendo does for the manufacturing process, parts, labor, etc. So at best, you might get a 3rd party option that would be the same price, or even more expensive than the official Nintendo version.
Even though Nintendo themselves did file for patents and were granted them. I know some company is either taking Nintendo to court, or alleging that they stole their design when it comes to the console/joycons. The pro controller I don't think Nintendo has a patent for. I don't think they are allowed to patent it when it has a basic shape, which has been used for quite some time now.
If somebody will produce it, then it'll have some defects like those third party controllers - for example lack of motion-controls. If third party make their Joy-Con with identical features, they will cost 10$ less then official, so there's not much profit for the scumbags.