At least IT and a BKN pick. Is the upgrade worth it and is it even an upgrade? Just because IT is shorter doesn't mean he doesn't have an impact on winning. The Bos roster isn't so amazing outside of IT that it is clearly better than Was. Is IT a clear downgrade from Wall? I don't necessarily think so. I would likely do a 1-1 trade, but including that BKN pick is a no-go for me.
Wall is also a legit two-way player who wouldn't be a deficit on that side of the ball and would actually make us scary with our perimeter D.
You also have to think that a Cousins trade would be almost guaranteed after a Wall trade. They have long expressed their desire to play together again, even recently. A Wall trade could force Cousins to ultimately try and direct himself to Boston.
That being said, I don't think he's available at all. Further, though I'd certainly do IT and the 2018 pick for him without blinking, since I think he's ultimately a much safer long-term investment than IT, he'd probably only marginally improve us by himself, and it'd mostly be just defensively.