I think you're spot on with the analysis of how social networks could be the masses' entry into the blockchain space. Whether that's a good thing or not is a different question. The content on Facebook for example is already mostly useless crap, so imagine what would happen if you could directly get paid for your activity there. I think it would lead to even worse content, as the system would incentivize spamming even more.

Another problem I see is the inherent centralization that comes with platforms such as steemit or EOS. The 'janitors' of these platforms in the case of EOS, or the whales on steemit just have too much power over the distribution of rewards, which leads to cartels and a plutocracy.
It is extremely important that the social networking platform that eventually wins the current race to mass adoption is sufficiently decentralized.