I think trading needs to be annoying, to discourage it. If they make it too easy and comfortable (like the AH in D3) it could very well cause the same issues to PoE as it did for D3. But I don't know if that is really the real reason, as I imagine determined players are going to use trading either way.
On a personal note, I'd love a balanced self-found league where drop rates are adjusted for a no-trading economy.