What with the increase in non English speaking players I think it would be cool if we could all easily trade together.
My suggestion is a new "Trade" tab in the GTL
Where you could list your Pokémon(or item) and also input what other Pokémon you are looking for, similar to the current advanced search system you could input everything about a specific Pokémon youre looking for down to the gender and ivs etc, also include a search option where you can drag your Pokémon into the box which will bring up all the posts that are looking for the Pokémon you have matching there specific needs.
Similar to GTL selling a Pokémon it will take your Pokémon away and list it for you, if someone accepts the trade both Pokémon are traded and need to be collected from the PC the same as a money sale.
Ty for reading :)