I have been following Steem for nearly 3 years now. It has been an interesting experiment. As a mainstream social network, it has been a failure. However, as an open market of content, it works. Not well, but it works.
Nevertheless, the question posed here is - does a social network actually benefit from being on a blockchain?
Let's look at what the mainstream social network audience want, and contrast it with what Steem currently offers - 1) Convenience. Obviously, Steem fails at this, it's far too complicated, there's no easy way to sign up instantly. Password recovery, account recovery, all far too challenging. 2) Content discovery. People just want to find good content and like-minded people to interact with. Steem's content sorting is not just suboptimal, it's almost worse than random. Steem is not a battleground of good ideas, but a game for the wealthy. It's a bizarre dystopia straight out of BioShock or Animal Farm.
Now, let's consider the purported benefits of blockchain social:
1) Censorship resistance. That's one perspective. Another is an invitation to unmoderated hate speech, illegal content etc. Most people don't want to read disturbing bullshit, they just want to find and consume the content they want. Steem can certainly form a niche among child pornographers and neo-Nazis, who would be banned elsewhere, but we are talking about the mainstream audience here. So, this is not really a benefit; rather a major drawback tying into content discovery - the lack of moderation and curation.
2) Privacy. This one is a misnomer. Steem has zero privacy by its very nature. 100% of every interaction you have with the Steem blockchain is 100% public and 0% private all the time. Anyone can do whatever they want with your data, at any time.
3) Tokenisation. Aha, so this is the USP for blockchain social, then. Dishing out inflation to content creators has proven to be unsustainable, however there's clearly potential to have a market of transparent advertising etc.
Moderation and curation are key to any social network. The first step would be to totally eliminate any common social space or reward pool. It's not going to work. Instead, one solution would be to create a blockchain platform, which can host various different types of social networks. Think Ethereum/EOS for social networks; rather than Bitcoin for social networks. Have one utility token, which will only be used to pay for computing resources/bandwidth etc. It'll also form as a market for attention etc.
On this, entrepreneurs can build their own social networks, and the free market will decide which ones work best. Some can be like Steem, some can be fully centralised; while I'd wager the successful ones will be hybrid that'll learn from the best of both extremes. Each can have their own UX, curation, gamification, moderation, tokenisation models etc. This leaves the burden of innovation on the free market, rather a group of disparate individuals who struggle to agree and get things done collectively. Who knows, maybe one dApp on this platform will come up with a brilliant idea that'll finally make blockchain social go mainstream.
So, why would they bother, when creating their own network could potentially be cheaper, especially the centralised ones? The answer lies in being part of a tokenised attention economy, assuming the base platform can foster one. It's a long shot, but it's the only way I can see a blockchain social network making any sense for the vast majority of people.