Yeah it's not worth the effort - smart TVs don't run on standardised hardware and every manufacturer has their own software so you'd have to do an absolute mountain of reverse engineering for a ton of different TVs. Plus they almost certainly require signed firmware so you also have to find an exploit to allow loading your custom firmware.

Far easier just to not connect the TV to the internet and use a third party solution like nVidia Shield instead. Fortunately pretty much no TVs will try to connect via open WiFi or 4G at the moment, though it is definitely coming.