It's probably best for the direction of this thread if we clarify that the role of an ISP can't really be replaced with a blockchain. At least, not in any way my brain can conjure. The clear impression I got from the OP is that the question was regarding "content" on a blockchain, such as websites:
I'm not sure if this exists yet, but if it does, it would totally decentralize the internet. Being blockchain powered, its content would become immutable, making it difficult for any government or nefarious organization, to take control over it and shutdown the websites living under such system.
So not the provision of access to the internet itself.
I do not believe that it will happen in the field of internet because internet is a service provided directly by the governments or organizations and without their control it is not able to run any service of internet.
Websites on a blockchain are already a thing. The only reason I haven't got one is down to laziness, heh.