I understand gavin, he prefers having less, but soon. The more general implementation (groffer's proposal) can substitute it later (v0.6 ??).
Yes, I want wallet security and backup as soon as possible, so I want transactions that support that functionality relayed and included in blocks as of the 0.5 release, if possible.
Current state: (old news for those of you on the bitcoin-development mailing list)
I've made a PULL request for "standard" (a and b), (a or b), (a and b) or c transactions to eventually support keys split between different devices, wallet backup, and wallet-backup-with-split-keys.
https://github.com/bitcoin/bitcoin/pull/541
Supporting lockTime or 2-of-3 escrow transactions or more generic 'standard' transaction in the future is certainly possible. Put together a solid pull request that adds support for relaying/including in blocks, with unit tests and a testing plan and, assuming there's general consensus that what you're proposing is safe and secure and is near the top of the "will make bitcoin better" priority list, it will get pulled.