@fugu13 would be curious to get your thoughts on this.

I see how it could be important to filter. Besides philosophical resistance to adding too much to the query API, and concerns that this will need a long interpretation discussion, I think this will be more difficult than it sounds for LRSs to implement (efficiently).

My biggest concern by far would be any confusion/discussion about the behavior, and if anyone is going to champion the "just filter activity type as written in each statement" approach I think it would be Russel, so curious to hear what he has to say there before I worry too much about the other points.