When posting, there are 3 options related to how a post manages payment: 50%/50% payment, decline payment, or 100% SP.
I suggest the introduction of a new option: "minimum comment fee". If author chooses that, then commenting will incur a minimum fee (0.1 STEEM?) or a custom one, as high as the author wants, set only for that post. If author chooses this option (which may be combined with any of the 3 above) then commenters won't be able to comment unless they pay that fee.
The comment fee may go to various places and, if this suggestion gets traction, I suggest a poll to crowdsource ideas. A few suggestions:
- comment fee goes to Steemit fund dedicated to the creation of new accounts (hence supporting the growth of the platform)
- comment fee goes to author 100% (as a form of tipping)
- comment fee is split between author and all commenters, on top of curation rewards
The rationale behind this suggestion is that many low-quality, irrelevant or spammy comments won't be posted at all, with a positive impact on the blockchain size and overall members experience.
The above text was posted identically, as an open issue, to the Steem GitHub repo.
If you want to contribute or debate, I would love to hear your ideas.
I'm a serial entrepreneur, blogger and ultrarunner. You can find me mainly on my blog at Dragos Roua where I write about productivity, business, relationships and running. Here on Steemit you may stay updated by following me 
https://steemit.com/~witnesses
If you're new to Steemit, you may find these articles relevant (that's also part of my witness activity to support new members of the platform):