You could theorize about all those things, or you could look at Codeberg, sr.ht or others that already are doing what you claim to be impossible, yet haven't took on VC money. People are signing up and using these already, despite not offering 100% the same features.

The aim doesn't have to be "Be the next GitHub", but something else, and that's just as valid and "successful" as anything else, as long as they survive as communities.