After much fruitful discussion and evolution, this proposal is now a series of "Bitcoin Improvement Proposals" -- see BIP 11, 12 and 13: https://en.bitcoin.it/wiki/Bitcoin_Improvement_Proposals
Sincere thanks to everybody who contributed improvements, ideas and code.
Gavin,
I have to side with coblee here. It's easier to maintain a general case than an expanding set of special cases. It also reduces the effort for third party tools (blockexplorer, android wallet).