Add Dwight Howard to the current squad, and we're one of the best teams in the conference.
I've been as down on the current team as anyone, but adding Dwight Howard would solve 90% of the team's ills. Rondo-to-Dwight would potentially be epic. Rondo would be (by far) the best PG he's played with - he'd be getting easy shots every night.
Pierce can still play. The reason GMs are calling about him (rather than KG) is that they know he can still be a very productive player for a few more years.
KG's probably not coming back (they'd have to renounce his Bird rights for the cap space anyway), but Brandon Bass could slide into the starting lineup - especially with Dwight covering up some of his weaknesses. Have to re-sign him.
Ray Allen, same as with KG, they'd have to renounce his Bird rights to re-sign him, but if he'd come back at the veteran min...
You could put up a lineup next year of
Rondo
Ray
Pierce
Bass
Dwight
That's pretty good right there, and pretty complementary pieces. Need a bench, but that wouldn't be a terrible place for Dwight to land. Need a bench still. Still a veteran squad, but where the age is showing itself mostly is in the interior - Dwight would be replacing JO (and to some extent, at least with respect to defense and rebounding, KG).
I think Dwight would at least have to consider Boston. It's still a tremendous longshot, but I think it's more of a 5% chance than a 1% chance.