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.
case 2 and 4 is effectively pointless, it's like a shitty lock, there's no point adding OR in the m-of-n mutli-sign. there only needs to be type 3 with extensions and type 5, ([1..n]) OR Z which is essentially type 3 with a master key.