I'd say two, maybe three. Beyond that, one wishes for a meta-platform integrating this all together.

(The same applies to IMs and groupchats. Personally, I can't reliably follow more than 3-4 channels, e-mail included.)

Also, all the legacy content creators are clinging to their old production models and airing shows one episode at a time. Just sign up for one month a year, binge, and cancel. Or do it twice a year.

Thousands of different platforms with some sort of federated subscription service.

Yeah, and that single site could proportion money to the content owners depending on how much their content is watched.

And to make it really simple and easy, the federated subscription service could build and maintain the streaming tech so that streaming experience is consistent across all platforms.

Just if this could exist!

This is pretty much how broadcast television works.

disconnect content distribution from the content licensing itself. That's the only way forward imho - each platform needs to compete on price and speed, not availability of exclusive content.