Sure, it’s being done. Xiaomi TVs have custom ROMs available, and I’m sure a bunch of others. Thing is, state of the art TVs are are not exactly cheap, and you need one to hack it in the first place. Most hackers do it for free, so they can’t exactly go on a spending spree.
ASUS RT-AX88U with Merlin firmware. Running stable since 2019 or so.
Edit: https://www.asuswrt-merlin.net/