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.)
So if Google (who once toyed with the idea of building their own internet) wanted to set up gcoin or PayPal for obvious reasons wanted to give birth to paycoin, (gee trademarking these wouldn't be a bad idea.) they could possibly outstrip bitcoin adoption rates. I once heard an ICANN rep say nobody would bother competing with them because of its adoption by world commerce. Bitcoin needs a fast adoption rate (like really fast) to survive as the standard. Even then corporations can start generating their own currency for gift vouchers, reward point etc.