Interesting thoughts. Before I address some of them, I'll like to say a big thank to @focusnow for such a clarifying post on steem communities. I belong to the @ocd community and fount it cumbersome to post directly from the beta.steemit\ page. I remember not being able to submit a post on the community site but easily submitted it at the main site.
About the points you raise regarding communities, I'll respond individually.
a) There are pros and cons to "whitelisting". For example, who decides a post is worth being seen by community members? Personally, I'll prefer using steemit's downvoting mechanism to rid off spam.

b)This will be quite unfair. Most people have multiple interests and might choose to post about several aspects of their lives in several mediums. Do this is almost equivalent to saying because you have a facebook account, then you should not have a linkedIn account. See the problem?

c) I totally agree with you on this one! The challenge will be linking the blockchain ID with the names we come up with. Can be done but I hardly see the incentive.

Overall, great post by @focusnow and great discussion you've started here @crypto.piotr. I'm hoping we'll hear other opinions.