To elaborate on this... I was involved in development of ArmoryX, an Armory modification which can do colored coins.

What I noticed is that it is fairly easy to implement plugins for Armory in Python. Perhaps etotheipi will add this to Armory mainline...

Anyway, it can look like this: you grab normal Armory binaries, then install some plugin in form of Python code (of course, you need to check that it doesn't steal your coins =) ), then you basically have "mix my coins" button.

It is fairly easy to implement this. p2ptrade I've implemented for ArmoryX does something very similar, so-called atomic coin swapping between two parties. (I.e. two parties construct a transaction and sign their parts of it after they check that transaction is right.)

It is probably possible to implement an add-on for bitcoind which would use RPC API.

Finally if somebody uses a client which doesn't have this plugin/add-on, he might run a standalone mixer program. Basically this program will give you an address, you send coins to that address, and some time later get them back.

So feasibility isn't a problem at all. I wonder whether this scheme is secure, and whether there is interest in mixing like this.