Last time that Tim made a move to keep Spurs compe ive, it wasn't exactly the same case. He just signed an extension that wasn't a max extension. This year, he will have to turn down first a $21.2M player option to sign for less money per year. It's a biggest personal investment. It would be also logical that Tim isn't thrilled to see that the paycut he took has been used to give a combined $50M to Jefferson and Bonner.
CBA wise, his new contract can be sign before July (it will be then an extension) or after July and a potential lockout. The max length allowed for an extension is 3 years. If the new CBA has the same over 36 rule than, the max length for a new contract will also be 3 years. I agree with you that waiting July and a new CBA to sign a new contract seems to be the smart choice because it will allow Spurs to have a clear picture of the financial situation but it's also somewhat risky for Tim to do so.
If Spurs wants to have an active summer to significantly improve the team, they will need to get some financial flexibility. Duncan restructuring his contract would surely helps a lot. A RJ for Childress trade would also allow Spurs to lower by $3.3M their 2011-2012 payroll. While I think Childress, thanks to his defense, could help a little more Spurs than RJ, the main edge of this trade would the gain of more financial flexibility.