I don't think you can actually make the trade because you can't turn around and trade Nance with other players. It has to be all at once.
That said, I don't think Cleveland does the trade. Walker is damaged goods and plays the same position as two recent top 5 picks for the Cavs (Langford does as well). They also really like Nance and have no incentive at all to trade him, especially with trading Love also leaving a gaping hole in their front court.
I don't mind the trade so much for Boston as we get to keep Smart (though 3 1st's is more than I'd want to pay giving up Brown), which is a big benefit. Harden, Smart, Tatum, Love, Thompson is right there with Milwaukee in the East and could challenge the Lakers or Clippers out west.