I'm not sure if a post limit would really solve the issue at it's core here. After all it doesn't take much effort to either post on alternate accounts or do your usual abuse via comments instead of posts.
I don't think there's any simple solution really. A powerful user here can only be stopped by an equally powerful user and only if that user is willing to use all their power just for that one person. Maybe a system to reward justified flags would help, but as it currently stands you'll always hinder yourself as well by using your vote power for flags.
There's really no clear cut where abuse of the entire system starts either. One person upvoting all their posts and nothing else seems really bad, but where does it stop? 5 people exclusively voting each others posts? 100 people exclusively voting each others posts? And how do you encourage people to vote for people outside of their comfort zone? I just can't imagine a scenario where there's not at least a decently sized reason to vote for yourself over anyone else.
And then there are bought votes, which I'm also not sure about. Originally I would have thought the 'promoted' section would suit the needs of people advertising their posts, but there's no denying that paying for votes that get you the same or more attention while also paying you back after 7 days is a lot more profitable. But honestly I feel like that's not really beneficial to have in the long run either. People who decide not to pay for upvotes end up having a really hard time being seen at all, while bad or mediocre content with bough upvotes flushes their posts all the way to the bottom.
Lastly there's the last minute before payout abuse, which is also really problematic. However from all the problems I feel like this one might be easier to resolve than the others. While it comes with it's own disadvantages I'd say this can easily be prevented by having the payout of posts happen not all at once but rather a fixed time after each upvote was used. That way there's no way to quickly translate voting power into cash. That could actually include the ability to earn from older posts as well, as I've always found it odd that older posts can't generate value anymore. You'd have to rethink a lot of aspects about this place though if that's going to happen. I'd be interested in seeing how people would go about this.
In any case I'm looking forwards to seeing what's going to happen, it's certainly something to talk about and discuss.
Quite a thoughtful comment.
I do agree that sneaky ninja selfvotes and botvotes at the last minute prepayout are a result of the 7 day payout period, which also renders posts with longterm benefit devoid of purpose. Who would publish 'Moby Dick' on Steemit? It's a strong disincentive to produce lasting content, which is counterproductive of Steemit's highest potential to benefit society.
Also, there are ways to incentivize upvoting others rather than yourself. Code is infinitely mutable, and while penalties for selfvotes are easily sidestepped, incentives to upvote others instead encourage behaviour that benefits the community, rather than trying to prevent behaviour that doesn't.
Consider the impact of increasing curation rewards for each successive account upvoted in a given day, week, month, etc. Coupled with strongly limiting bots, such an incentive could radically impact curation, and thus rewards for content creators.
Thanks!