You already have the ability to refuse. Don't use the product. I agree that is a lousy answer but it is what it is, at least for now.
On the other hand, the rest of what you're suggesting is not a bad idea. That may be possible. It would void the warranty on your hardware but many have made that sacrifice willingly with many devices. It would actually be cool to be able to install an open source OS on Roku's and other similar devices, and it wouldn't surprise me at all if there's already teams out there somewhere already building open source alternatives to big name streaming device OS's.
Have you Googled it? I'm guessing probably and you didn't find anything yet otherwise you most likely wouldn't be here discussing it. There are quite a lot of folks out there discussing it. Discussions like them usually develop into, well, actual development. I would keep an eye out and look around. Something will probably start popping up at some point.
