I've been thinking the same exact thing recently but for different reasons. I've been using the steemconnect 2 SDK and noticed this in the "follow" function:
json: JSON.stringify(['follow', { follower, following, what: ['blog'] }])
Notice the "what" property is set to "blog". This implies to me that there is at least some level of thought / support for posting and following things other than the "blog".
I haven't been able to find any more information about this or if anything other than "blog" is actually possible at this time. I'm guessing it isn't.
Having a messy blog on SteemIt is annoying, but this issue will present much bigger problems than that as more 3rd party sites and SMTs are released.
I'm planning a post about this as well and hope to really get through to the Steem developers to make sure they understand and will address this problem.
I am following you now but please be sure to post the link to the post in one of my blog posts so that I see it....I would like to read what you write about this topic.
It seems that in the code you posted, they just need to change that to ['comments'] for the time being. At least then all the third party apps would end up in the comment section which would be tolerable.
Thank you for your sharing what you uncovered.