I see a lot of downside. The proposal appears to be: Thornton, Fredette, Hickson, 2012 1st rounder for Deron Williams.
First, I'm not sure we can actually trade that 2012 first-rounder at the deadline, because we've sent a conditional one to Cleveland in the Hickson deal already. Even if we designed some clever "this year if we have it otherwise some future year" deal, I think that would still fall afoul of the Stepien Rule.
That aside, there are two big problems with acquiring Williams. One, he almost certainly doesn't want to play here. Two, he's got a player option this summer, and he'd walk. Hickson is not the problem here, but we're talking about sending away one of our few decent contracts in Thornton, our 2011 first-rounder in Jimmer, and another first-rounder (keeping in mind that we are already one future first-rounder in the hole). We're talking about not only sending away Thornton, but getting zero value from three first-round picks over a 3-5 year period for a two-month rental of a star who's not going to be able to get us into the playoffs because we're too far back? And there's no downside?
The way things are going, unless the Nets swing a trade for Howard, Deron is going to walk at the end of the season. We can try our luck in free agency and see if he really would want to come here (I doubt it). But let's not throw away essentially the sum total of non-untouchable assets (read: not Tyreke/DeMarcus) that we have on a hail mary for the 8 seed this season.