Problem is that this league is littered with talented scoring point guards. We're in the midst of a point guard boom.
There are at least 6 who are arguably better than Rondo and several more of comparable talent.
Clippers - Chris Paul
Thunder - Westbrook
Spurs - Parker
Warriors - Curry
Cavs - Irving
Philly - Holiday
Brooklyn - Williams
...
I doubt any of the above teams would be interested in trading their Point guard straight up for Rondo.
Additionally you have:
Hornets - Vasquez (averaging 14, 9 and 4)
Portland - Lillard (one of the best young guards in the league)
Bucks - Jennings (23 and still improving)
Denver - Lawson
Toronto - Lowry
Timberwolves - Rubio
Washington - John Wall
Houston - Jeremy Lin
... FOr all of the above teams, I feel like it would be a tough sell. None of the above players are perfect, but neither is Rondo... and I imagine they'd have some debate over whether or not it was an actual upgrade or not.
There are teams like Utah who clearly need a quality PG (although they'd probably prefer one who could shoot so they could spread the floor enough to let their bigs do work down low)
The list starts to get really short. It's the reason why Ainge has been unsuccessful in trading Rondo despite shopping him every year. Teams around the league see him as a flawed player who may be the statistical beneficiary of his system. A lot of teams already have point guards they are content with. And a lot of teams are content not having a star point guard in the first place... they'd rather hang onto their talented bigs and talented scorers than trade for a flawed passer. For example, add Miami to a list of teams who doesn't give a crap if they have Rondo or not.
So I imagine the list of teams who would "kill" to get Rondo is pretty short. And of those teams, I'm not sure how many of them have an asset we'd be that interested in.