I think adding this would be quite the quality of life feature! I wasn't aware this wasn't a feature until I made a forum post myself and realized I wasn't getting any notifications when I was getting comments/replies under my forum post. If you're the OP (original poster) of the forum I believe you should get notifications each time someone comments on the post. Additionally, to help mitigate clutter, I think "threads" should be implemented within the forums, wherein if someone wants to respond directly to a comment made by someone, they can respond to that comment directly, thus notifying the person whose comment they replied to directly. Something else that may help to reduce clutter and or mass notifications is giving Users (whether it be the OP or those under the comments) the ability to mute future notifications and or replies under the post.