This may sound really weird and dumb (and long, on top of that) to you micro-pc gurus but this thought has been going in my head lately so I'd like to ask to someone who actually knows. Please excuse me in advance.
I have a Sony Bravia 'smart' TV, pre-Android TV (and pre-Google TV). It still works great, if I'm not wrong it just completed 10 years with me (or it's about to be 10 years old).
The thing is that, along that it takes time to "warm up" when turning it on, it has a non-updateable WebOS or something similar. An ecosystem that seemed to be rich at first now barely has a youtube app that works veeeeeeeeeery sloooooooooooow (it will hang and crash after a couple videos!) and, worst, you can't block its ads (maybe partially with a PiHole but it seems YouTube won the war in that front).
Of course I know I could just use a Chromecast or whatever, but I don't like the idea of having yet another device plugged in, an ethernet port in the TV that would render useless, and another remote control to take care of. I "still" use my TV to, well, watch TV. Like antenna/cable stuff. I don't even have a single subscription streaming service (Netflix, Hulu, Disney+, etc).
Plus the idea of buying a new TV kinda goes out of the window - new ones cost 4x for what I bought this one, this one still works pretty well (the issues are most software related), and the new Sony-s that arrived here don't even have the internal DVB-T2 antenna so I won't be able to watch local TV.
Ideally I'd like that when you go to the 'Home' section of the TV (where you can launch apps, navigate the gallery... that kind of stuff) it gives the control to the Pi instead, and you always could go to the 'TV' mode as usual (in other words, giving the image/sound control back to the "original" OS).
So having some idea of what a Raspberry PI is capable of, I'd like to ask if is it possible in some way to hack the TV to replace whatever system/board/etc controls the TV with a Pi? I can imagine the answer being 'no' due to propietary buses or connection incompatibilities, but will that be the case for every single TV, or is there some standarization about it?