How hard would it be to market a new blockchain? Would it be as hard as competing with ICAAN and starting up a new separate internet using a different protocol?
no, it would be more like setting up a blog that competes with an existing blog that has a readership of about 10,000.
it's a little harder than that because some bitcoin
services, like exchanges, are hard to set up. thus, in practical terms, you'd eventually need buy-in from mt gox or the ability to start a new exchange. that said, the lack of transparency for, and competition with, mt gox is a significant problem for the current block chain anyway.
if a company like dwolla wanted to set up an alternative block chain, they could do it very easily and have a good chance of gaining more adoption than the current block chain has done. the current block chain needn't stand up particularly well to anyone with even a modest marketing budget. (i just hope that person or company wants to use the bitcoin technology rather than something else.)