To elaborate on why Golden State would do this: I believe they will be looking to unload Lee's salary so they are able to re-sign Draymond Green. Also Klay Thompson has a contract extension that will kick in soon.
I think it would be best if a Ainge finds a contract that fits within the 12.9 mil range we have for the traded player exception (TPE). McGee works, but I have some doubt that Denver would be willing to offer a first rd pick to get rid of him. They are not contending and their 1st rd picks would be too valuable to trade.
With that said, maybe Ainge can squeeze out another "conditional 1st rd pick" that turns into 2 seconds. In return the Celtics take on the immediate cap space and send two serviceable role players on expiring contracts to Denver in the process.
Bottom line: any team which possesses a player who has 2 years left on his contract (or 3 yrs w/ the final year being a team option) could offer Boston a conditional 1st rd pick for expiring contracts. The player can't be too talented (i.e Nicholas Batum) unless Ainge is willing to give up assets in the early stages of this rebuild.
So essentially the team trading with the Celtics would be getting expiring contracts & a trade exception up to 12.9 mil. That trade exception could be valuable to a team like GS who might be looking to add another player in the offseason. With the TPE they could add another player w/ a large salary or two players w/ smaller salaries.
These are trades that happen over the summer. Golden State has the best record in the NBA, and is under the luxury tax. If they want to move Lee to keep Green, next summer is when that happens, not now. It will be a cheaper price to move Lee at that point, and it won't disrupt a team in the middle of a playoff run. There's no reason Golden State dumps Lee in February, unless he tears an ACL or something. Just makes no sense. Same with all your other proposals-- you move those guys when a better way to spend the money presents itself, and not before. This is why Gerald Wallace is still a Celtic.
I sort of disagree. Golden State has played most of this year without Lee and has been winning. This shows that Lee isn't as crucial as he once was proclaimed to be to GS's core. There would be little to no incentive for the Celtics to trade for David Lee in the offseason unless it involves us getting picks. Bass & Thornton's contracts would officially be coming off the books so the C's could no longer offer up their contracts.
If both teams wait until the offseason, the only large contract Boston would have to offer Golden State is Gerald Wallace. Both Wallace & Lee have contracts that will expire in 2016. Golden State would have the most incentive to do this trade since they would be saving approx. 5 mil in the 2015-2016 season.
Why wait until then though? Trade Lee to BOS now. GS was rumored to be interested in using their TPE on Bass, but opted to let it expire instead.
By trading Lee to BOS now GS gets two good role players on expiring contracts who could either be kept or re-traded (in 2 separate 1 for 1 trades only) for another player with an expiring contract and a second rounder (Toronto---Bass for Hayes & a 2nd / or Thornton for Fields & a 2nd?). Maybe GS replaces Lee w/ Bass and trades Thornton. They could trade for another expiring player and agree to a buyout w/ him due to lack of available playing time. That would not only save GS money next year, but more money this year as well.
IMO do the trade now or not at all...Wallace could be traded next year the same way I'm proposing we trade Bass & Thornton this year (as an expiring) to get Lee & 2 seconds. Why settle for a trade like Lee for Wallace and second in the offseason when we could make a trade now and get a conditional 1st for Bass & Thornton, and then turn Wallace into another conditional 1st at next year's deadline?
Ainge will be looking to getting more assets so it makes sense for him to trade his expiring players for some before they become Free Agents.