Is this in MVP?
Yes. As soon as there is user content, people will want to agree, criticize, discuss, etc. If we don’t provide a way to do it, people will use the answer box, and that defeats the purpose of Q&A because we’ll have lots and lots of non-answers.
On the other hand, I don’t think anything other than the ability to post comments is MVP, including voting, hiding and notifications.
Refining the requirement
SE struggles with comments. They have a high cost in moderation (variable depending on the site culture).
A vocal minority keeps complaining when their comments get deleted. The rules say that comments are ephemeral, but people tend to think “but mine is oh so important”.
I propose to design comments in such a way that deletion is exceptional (basically only for rude/non-constructive) but visibility is low. In the SE model, that would roughly mean that each post automatically has a chat room (except without the bit where people can see that you’re in the chatroom), but selected chat messages are automatically visible. We don’t delete obsolete comments, we just downgrade their visibility.
For MVP, I propose to start with just a chat-like thing which does not notify the post author. Show only a link to the discussion page, or show the discussion in a small area with a scrollbar. Then later we’ll build visibility and notification mechanisms, based on experience using the system.
On distinguishing requests from feedback
I don’t understand the distinction. The difference between requests for clarifications and improvement suggestions is mostly a matter of phrasing — “can you explain this?” vs “I don’t understand this”. Unless you mean definite improvement suggestions “this should be that instead”, which should be edits, not comments.