This is the intriguing part of BTC. What will be able to plug into the block chain for authentication purposes? How does that affect future transaction fees as miners make less BTC rewards and want to be compensated for authenticating transactions? Will future price of BTC offset that?
I've been advocating for a long time that we declare a minimum transaction based on the cost of electricity and the fee to pay the miners and use that as a base transaction for colored coins. There is only a 40 bit block reserved for metadata in the blockchain itself, but that is supposed to be enough to color a coin to authenticate a share of stock.