In theory, this is already possible. Anyone can patch the client to reject transactions containing such coins; the key is getting enough adoption for it to be m

In theory, this is already possible. Anyone can patch the client to reject transactions containing such coins; the key is getting enough adoption for it to be meaningful. (I imagine starting by forking mining-specific applications like cgminer would be more effective than forking the client apps, since you really want to get 51% of the network to reject these transactions for it to mean anything.)