First off, nice article. Very clear and informative.
I don't know if this is the best place to post this, but it seems related to me.
As more wallets implement BIP32, I believe that bitcoin wallets should begin to encourage people to use
https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki#recurrent-business-to-business-transactions-mi0 style address instead of traditional addresses. In the end, this would improve privacy because users never need to merge coin if they had one of these "super addresses".
In addition, "super addresses" would fit nicely into BIP70. Right now, the PaymentDetails message allows the merchant to provide multiple outputs. If instead the PaymentDetails provide 1 traditional output (for reverse compatibility) and 1 "super address", the payment could be broken into as many pieces as is needed to match unspent outputs already in the customers wallet. Finally, the refund_to address in Payment could also be upgraded to a "super address" to enhance privacy there.
I am not sure if there is a large memory requirement for "super addresses", but to me, it seems that a lot of these privacy enhancing possibilities will be simple to implement once BIP32 is widely deployed.