One problem I see is that if one user uses multiple sites built on Steem, will this user understand that he can login to all of these sites with the same account? I already see some people speaking about "Steemmonsters accounts" and "Steemit accounts", they think those are different things and not the same and sometime create multiple accounts because of this, although they would use one, if they knew that it's possible. Maybe this is something solveable through a social-media-login like approach (e.g. Google/Facebook login, just with Steem). Something similar to Steemconnect or Steem Keychain, I guess.