While this will limit spam, I think it will also limit the quality posts from genuine people too. But I agree it's a good method... It's just one that's easily abused...

If the fee goes to the author, I'm pretty sure most people will make their posts need a fee to comment on... If it was dedicated to steem development I don't think this problem will happen.

I think this is a good solution, but will create new problems so I hope people brainstorm on it to make the (close-to-)perfect solution.