That's not a bad idea, a soft cap based on reputation. It would certainly slow new automated accounts from getting up to speed. The cap could be pretty high as well. 99.9% of users don't post anywhere near these volumes.
We're fortunate that the Steem blockchain can handle a really large volume of transactions. I think on other blockchains these volumes would be a much bigger issue. As steem reaches mass adoption this could potentially become a bigger problem so it might be wise to trial a few things while we have the capacity.