This is the sort of trade that a rebuilding team should seek to make, renting out cap space for assets. Golden State has shown they don't need Lee to win and would like to get out from under the $15.5 million owed to him next season so that they can pay for Klay Thompson's extension and retain Draymond Green. Golden State has had reported interest in Bass in the past and might have used their trade exception to grab him if the possibility of a Kevin Love trade had been taken of the table before it expired.
The question is, what to put with Bass? A second round pick would replenish the bare cupboard of Golden State. Thornton makes the math work. Brandan Wright would probably be more useful to the Warriors, but can't be aggregated with Bass in a trade until closer to the deadline. What about a trade where Green is shipped off to a third team?
The key is how desperate Golden State is to shed future salary and how willing Boston is to have a $15-million man coming off the bench.