Also, batching filters might result in unintended expansion of result set - instead of 2 filters {npub1,kind1} and {npub2,kind2} sending one {[npub1,npub2],[kind1,kind2]} may return much more than was needed. So it seems like relays should allow more of precise (smaller?) filters. 

 Yep, batching like I do creates much more complicated queries for their indexes to deal with. It doesnt make any sense.