I agree. Comment rewards probably don't need to be designed into the blockchain. Most likely commenting can be encouraged by the front end design & purpose of a website. A Quora style frontend for Steem will naturally encourage commenting, but the platform can still be effective using the same reward pool. Also 38% seems way too high. Building a comment pool with such a high reward pool will probably turn Steemit into more of a Quora or Reddit instead of a Medium-style blogging platform immediately. It would be an interesting experiment, but again it's better to leave everything up to the frontend.