Never will happen. Sacramento could do better.
I can see Sac wanting to trade Cousins/Evans, and they don't exactly have a ton of leverage, but the deal as proposed lacks a good big coming back. Sac will likely be looking to get a center.
I think a deal involving Utah might make the most sense.
Bos- IN: Cousins, Salmons
OUT: Green, Bradley, Sullinger
Sac- IN: Jefferson, Green, Bradley
OUT: Cousins, Evans, Salmons
Utah- IN: Evans, Sullinger
Might require some picks heading to Sac, but I'd say its fair return for all involved.