Ok, the base of the idea here is to alleviate three problems with the trading of PoE.
First, the item link limit
Second, the spam caused by linking too many items
Third, having to alt-tab out of the game to check someone's trading list.
To start with, everyone would be able to check an item in their stash as "up for trade" or not. Every single stashes would have their own special link that could be copied in the game chat and that would open an in-game window showing every single "up for trade" items for that player.
The items could either be manually sorted or done automatically.
You could also browse the selection from the forum by copying the stash link into a message.