I have a smart TV as well, but refuse to connect it directly to wifi. As I tried that when I bought it and it insta-bricked itself and had to go through the hassle of returning a delivered TV.
A custom ROM for this device would be interesting. I know that the Chromecast 4K can do a custom ROM, but only if it was running an older os version before you flash it, as the bootloader couldn’t be unlocked after.