Hi David,
This is an interesting one - have never come across this before. You are correct about the activity notifications, as that wont work since this is not something tied to an activity of some sort (which would have an activity association record tied to it). There is an existing activity for "New Follow-up Comment" that exists out of the box, BUT, I dont think that there is a way to get it to do a "reminder" of sorts for open comments that are greater than 30 days and not closed. I tried to set this up before responding to you by creating a new site-defined-condition, that being that the open KD comment is more than 30 days old and is still open, but I cannot get it to work I think your best bet for this would be to create an idea here on the community, OR, just use a report to pull it. The table you need is :O_COMMENTS" and the field is FLG_STATUS, which would be "Open".
Hope this helps a bit.
Thanks,
Jon I.