Nowadays with the brain damage that has been inflicted by adtech social media over decades it is hard to imaging mass adoption of such a publicly funded outlet. People have become literally social media junkies. Unless you do a tiktok like race to the bottom you can't disrupt the incumbents.
But establishing the principle is important even if its a small audience. 2% of billions is still a large population. Just like public TV being typically of higher quality (where it exists) such platforms could be really interesting, worthwhile places.
If the experiment succeeds one can start thinking of introducing user fees and other funding mechanisms and eventually maybe restoring sanity and delegating the targeted adtech industry in the darkest corner of hell where it belongs.