[As I currently understand it, the problem is thought to be a limit on the number of locks on the BDB database, which is in turn a function of the number of transactions in a block and/or the number of transactions referenced by a block, which is indirectly related to the size of a block.]
There is some evidence from other threads that it might be possible to fixed old clients by adding a single configuration file, without requiring any code updates at all.
I am aware of that. The problem remains. Any 0.7.x (or prior) client that hasn't upgraded or updated the BDB configuration file will soon be on a hard fork of the block chain. Aside from the risk to those individuals, I think that would be extremely harmful to the overall credibility of Bitcoin.