Rondo is a special player, but he needs a special supporting cast: basically both wings and the PF need to be able to space the floor. That's due primarily to the fact that he does not provide a lot of spacing, due to the fact that he is a poor 3P FG shooter.
As such, if the Celtics are going to build around him, they would be in a better decision to make personnel decisions if they knew he would re-sign with the team. Likewise, if Rondo wants the best shot at winning, he would put himself in the best position to do that if he would agree to re-sign with the team.
His own shooting deficiencies are the cause of this. The fact is, he will not be traded to an elite team, and, if he wants a max deal, only a non-contender will be able to afford to give it to him (Houston will re-sign Parsons to something big).
Rondo ought to double down, take his max extension, and commit.