He has an awful contract starting next season, so that automatically lowers his trade value. However, if Washington is ever going to trade him, now may be the best time, while he has a more reasonable salary to match this season.
I think a team like Milwaukee should take the chance, as their not exactly the mecca for free agents to sign. I know the Buck are playing really well right now, but Wall may be the difference in advancing in the playoffs. Wall for Eric Bledsoe (expiring), Thon Maker, and Donte DiVincenzo.
This will give the Bucks a big 3 of Antetokounmpo, Wall, and Middleton.