No!
Communism had always been about fully centralised control and full power. No way it could be anyway libertarian.
I would actually have to disagree with this. Don't get me wrong, communism is flawed, however, to say that that if has to be centralized and is incompatible with libertarianism isn't true. Many communist movements have adhered to democratic principles and have supported decentralization (heck, "soviet" even translates to "workers' council). Communism is also extremely broad, ranging from anarchists to ultra-totalitarians. To say that all communism is totalitarian Marxist-Leninism is like saying that all socialism is communism.
Anyway, in order for the Union of Soviet Socialist Republics to be democratic, you would need different, more libertarian, leaders of the pre-Russian Civil War Russian communist movement. Replace Lenin with someone who endorsed democracy and libertarian socialism. One particular idea that I like is making Rosa Luxemburg stay in Poland after forming the basics of her political views and proceeding to fall in with Russian communists. Is it the most plausible scenario? No, but it's a fun change, in my opinion.
As for what a democratic USSR would look like, I can see it being more syndicalist than communist. The means of production would be controlled by the proletariat via unions of workers (they would probably be called soviets ITTL), and I can see some mutualist elements being thrown in as well.