Hey Billy,
I think that at one point in the past we had this, not 100% sure thought. I removed it, because I couldn't make it work all the time. You see each component comes with a different category id column. For some it is category_id, for others it is cat_ids etc. And not only that, but if I were to filter on the cat id I have to complicate the query and do a join over the target table and filter on the catid there as the only thing that we care about in the #__comment table is the contentid.
Now that I'm explaining all this I remember, that we had a filter on catid and it was only working for com_content. That's why I removed it.
Are we talking about com_content or another component?
Regards,
Daniel