Replying to your last comment (comment tree limit).
An obvious benefit of curation guilds I didn't mention in my last comment is that curation guilds encourage and organise organic voting. Previously, people would just vote for whatever was profitable, generating bot swarms behind a very select few users. Of course, these bot swarms still exist, but curation has diversified greatly.
With curation guilds it's much more profitable to vote on good content, because they know a curation guild will be looking out to vote after them, so they can cash in greater curation rewards. (Needless to say, it would be much more profitable to vote on a post with few rewards generated than voting on posts which already attract bot swarms).
We can see this complete change in behaviour - even bots now look out for popular content (i.e. lots of votes with but very little payout). The top two bots by curation rewards - @biophil and @better (laonie) follow a similar algorithm.
So, curation guilds are just as essential to promote organic voting - which is definitely essential, as you mention.
That's a very good question! When I first took interest in curation, personally my chief goal was to retain users. It sucked to see thousands of users exit the platform en masse because they were offered no exposure or rewards. My initial thought was there would be a point at which curation guilds won't be required - I used to joke about "Curie being successful when there's no need for Curie".
But the more I work with a curation guild, the more I see other curation guilds like Steem Guild, the Reddit tag project, Steemtrail form; the more I realize that this may be the only true USP of Steem. Authors do get rewarded in other social platforms - whether by attention, exposure or engagement. But not curators (upvoters/likers etc.). Steem may be the only social network that actually rewards curation, and I have seen many people take interest. I'd say 10%-20% of the active user base are also active curators, and this does not include bots. I'm pretty certain (it would be logical) that they vote more diligently since there's a reward involved. (The of course - I hope the algorithm is fine tuned) I have also seen the enthusiasm and passion shared by many curators first hand - they are as involved as top authors and commenters. Curie really encourages this - our #curie channel is arguably the largest collaborative project in the community, with a hundred people collaborating every week.
So maybe curation guilds should stick around - if Steemit ever attains critical mass, it's going to lead to a better platform than Reddit, where there's a real problem of good content being undiscovered. One may argue that a curation guild would have a greater, more important purpose when there's volume - as then there will be truly great posts chosen. To add further, as a long term Redditor I can totally see how Reddit desperately needs a curation guild - but why would they take the time and effort to form one without the incentive of any reward?
Of course, I'd like to see a better allocation of R-shares, away from the top stakeholders to the top curators. (I have proposed a curator's reputation system previously, which would also weed out the greedy bots and naturally prevents Sybil attacks) That'll make curation guilds much more direct, doing away with the seemingly "corporate/top-down" nature which I totally understand why the community would be distrustful of. For now, we'll just have to work with what the network offers.