A post limit, especially only 4, is completely unworkable. Others have already brought up that it does not defend at all against multiple accounts, but the main problem is the Steem vs. Steemit distinction.
Any limit would need to be imposed on the blockchain level. One of the main strengths of Steem is the unified account & identity across multiple applications. In a day, I could easily make 2 Steemit posts, 4 quick Zaps, add a couple photos to my Steepshot page, update a project on Utopian, post a vlog to dTube, and end the night relaxing by throwing a meme on dMania and streaming the video game I’m playing on dLive.
That’s 12 posts, completely non abusive. The 4 post limit may have been fine when Steemit was the only platform, but it’s gone for good reason.
This is what I was saying, but you said it better. I really think many on Steemit don't realize just how many platforms are included in the Steemit ecosystem. You named a few I didn't know about as well. We all want Steemit to grow, as you said that is the strength of the Steemit platform....many platforms in one.