I believe it is possible by simply attach a rooted device to the TV with streaming capability, like a computer, or a rooted nvidia shield.
Although I don't agree with OP that everything needs to be rooted, for example, my phone runs grapheneos without root, I do believe most rooted OS are more usable than proprietary OS like Roku.
It can still stream video over the hdmi port just fine. This is about containing the rooted malware inside the tv's firmware from exfiltrating and then self destructing.