A lot of times readers add some useful comment relating to the post and the author might want that to be highlighted and not be lost in other comments. Youtube has a feature of pinned comment, so this would be similar to that.
The UI can be similar to how pinned articles look on the profile!
Also I'm not aware if there has been similar feature requests, I didn't find any on my own so I opened this issue. If this is a duplicate or this feature is already in the works then please close this
PS: Dev.to is awesome