Please let's just try and use the tools Satoshi left us with rather than constantly trying to change them. I'm strongly against trying to "improve" parts of the protocol that we've barely even begun to understand yet, like nLockTime and tx replacement.
Some of the big mining pool operators are already going their own way, experimenting with new types of transactions (e.g. deepbit and eligius), so I suspect the answer to your question "Can 'we' please hold off..." is "No."Discussions like this one are how I start to understand parts of the protocol like nLockTime and transaction replacement better.
As for BIP 16 draining effort away from making the standard client scale: I've been saying for a year that my top priorities are network stability and wallet security. Making the standard client scale is, in my opinion, a lower priority; I don't want a super-scalable client with a 4-minute blockchain initial block sync time if it is vulnerable to the user clicking one wrong link and getting infected by a trojan wallet stealer.