Nope, no way. He has the most tradeable contract on our team. People often say "We should keep X for now because their value will increase at the trade deadline" Of all those players, ET will see the biggest increase in value. He'd be a perfect compliment to a lot of contending teams at the deadline.
Except that the last time he got traded at the trade deadline it was for the corpse of Danny Granger and a second round pick -- and that was after he was having a better year in Philly (17.5-6-4 assists? or something like that) than he's likely to have in Boston, as well as being in the tantalizing position of RFA, so Indiana could keep him at all odds if they cared to.
Of course, it turned out that he was one of the two primary factors in the total dissolution of the Pacers (depending on which rumors you believe), and wasn't a meaningful contributor to a team that was aiming at the ECF.
So, I'm not sure that what you're saying has a very strong basis in reality.
Also worth noting: the 76ers tried to get a first round pick in exchange for him forever... and they settled for the deceased Mr. Granger and a second-rounder.
Zeller was traded for a trade exception, IT was traded an expiring Marcus Thornton and a late 2016 1st, David Lee was traded for Gerald Wallace... that list could go on forever. What happened in the past doesn't mean that will be their trade value next time. On top of that it is clear that ET has had his best season in the NBA with the Celtics and is on an expiring contract. Both those things increase his trade value.
Last season Turner was one of our most clutch, most consistent, highest level players. It just baffles me that people would trade that for 2 second rounders. I don't buy the arguments about blocking growth. Even if you bench him until an injury comes along he's better value than some of the others.
Zeller's one of the last players on this team that will go in a salary dump. Even backup centers are tough to find in this league, nevermind one's on cheap contracts.
I don't think Danny will salary dump, I think he'll find a trade worth doing. But if he does have to, Zeller is way down on the depth chart and will be a restricted free agent next year. Presumably his salary will increase after that negating your point about a cheap contract. Guys who can go off for a triple double are rare to find as well. Also we do have a gajillion picks we can use to develop a backup big if we need to.
I get its not a simple decision. ET is a great trade chip NOW. But I think he'll be better value in the future. But I just can't get behind the idea that one of our better players gets dumped because "We need to invest in our future", particularly when Danny seems focused on the now as much as the future.