It would be nice to have the possibility to filter item listings in the GTL, just like we can do it with Pokemon (but of course with different criteria).
This idea originated when I was looking at vanities/clothes in general, but couldn't do it in an easy way - I could either watch the whole list of items and try to find vanities among them, or use the name filter one by one (both methods annoying).
So, the first thing that comes to my mind is filtering by Bag categories (Items, Poke Balls, TMs & HMs, Berries, Cosmetics).
Another idea, though I'm not sure about it and it needs discussion, would be a subfilter for the Items category, which is quite generic at the moment. It could be divided into Stones, Potions, Type Enhancers, Rubbish, lol I don't know really. This could be a little harder.
Waiting for likes & opinions