Some startups will grow very large and become very valuable and will stay around for a long time.
No cryptocoins will be around for a long time. They are all going to crash to near worthlessness, including Bitcoin and Ethereum.
Also the idea of Webvan was not a bad one, they were just too early. People put too much money in too early to a good idea.
Cryptocoins are not an idea before its time or of its time. It is inherently a worthless thing. Just like quack medicine was worthless a century ago and is worthless now.
Are you suggesting cryptocurrencies are banks? Please explain that logic. I also suggest you read up on the tulip mania [1].
Note: I do think bitcoin has value for illegal transactions but that's the only place I see cryptocurrencies solving a problem more efficiently than current solutions.