Personally, even though a library isn't necessarily a means of production, I don't think it would be not be welcomed under a communism environment. I feel the concept of a library and how they work overall is similar to what communist might be looking for in general from such a service.
The thing about rumble is, they'l allow pretty much any kind of Speech, but if you are left leaning i'm thinking (hoping) they would treat you the same as the right. That is something I think someone ought a do a documentary about.
Does Rumble really care about free speech, or is it strictly the alt right speech? For reach, surely Rumble wouldn't be bad, in fact probably your next best for viewer reach next to Youtube and Twitch.
Personally I don't use Rumble but I understand you got to do what you got to do to get viewership.