I'm pretty sure that looks better on paper than it will do in the real world.
Today a lot of software libraries are incorporated into applications. These libraries solve specific problems that the vendor didn't have to solve themselves. Often these libraries are licensed to be used under specific circumstances.
Even if you would get your hands on the source code, you are certainly not allowed to declare it open source.
So even if Sony were to release the OS on the Bravia as open source, it would most likely be a Swiss cheese with holes that had to be fixed before it was usable.
At that point you still wouldn't have gained much from an end user perspective since there is still no app store. Even if you set up your own local app store you would have to convince Netflix and other streaming services to release a client app for your tv.
I think the solution is more in the direction of legal pressure. If you sell something, it should be expected that you honor that sale and not change it to something it wasn't when you happily accepted the money.