Well, even though I am not sure it would (because that OS would surely allow http requests, right?), there is no incentive for manufacturers to use such an OS,

Well, even though I am not sure it would (because that OS would surely allow http requests, right?), there is no incentive for manufacturers to use such an OS, at least yet. I can't really think of anything that would change this situation -- although IoT devices will get more sophisticated, they will likely remain quite single-purpose, with webapps or mobile apps serving as the UI, so there isn't going to be much to gain from a large common code base.