Not a proper alternative really. Some of your own set up too, you could buy a laptop or small form factor PC? Lots of great Linux distros to get on there.
I have done that in the past, using a raspberry pi. I was using Plex (Rasplex) back then. The main problem was convenience, mostly with the possibility to have proper remote control from the couch.
For just myself, this could possibly work, but it’s a non-starter for the non technical people in my house. They need a remote control on the couch and the ability to easily open different streaming apps with that.