There is no evidence that is clear Ainge wants to move Rondo. There is also no way Dumars would even think of moving Drummond. But if he had to choose out of the 3 big men, Drummond would most likely be the one on the trading block. Monroe has a good skill set for a big men, nice mid range, can actually shoot a free throw, and has promise to be one of the top 5 big men in due time.
The problem is Dumars is like the Nuggets, but relatively better. He has a influx of big men, but no spots for them to really take control, and be situated in a starting spot. Drummond can start next year in my opinion, with the way he's been playing last year, and in the SL. It is no doubt he was one of the strongest players in SL, and could've easily done much more damage had his minutes not been reduced, or games sat.
Dumars need to start realizing he has good pieces. If I were him, I'd stick it out with Knight, who defensively is rising up in the ranks. If Smith wants to complains about the lack of a true PG, then I'd put him on the trading block. He may be in his prime, but as far as I'm concerned, Smith is the lesser of the two. Defensively he's the strongest anchor, but once his prime is over, and his athleticism wanes, there isn't much to his game.
Smith may be requesting that Dumars goes for Rondo, but Ainge is certainly not going to trade him for anything less than a superstar or a franchise player. The Pistons have no number one pick, and Ainge is clearly re-building and tanking at the same time. You don't rebuild without getting any picks or anything else of equal value in return. Drummond has huge potential, but it isn't exactly proven on the big screen. Ainge knows this. He could be a bust, or he could be the best big man in a few years.
There is absolutely no proof Drummond will ever become top 5 big man in the future. Just the potential, which isn't enough to warrant a trade as of yet.
I'd build up Rondo's true trade value which is nothing less than a top 10 player in the league for him.