Bitcoin is flavor of the month.

It's possible to conceive of a better cryptographic store of value (imagine a more deflationary version of bitcoin with close to zero coins generated on the network that requires 2-step verification in order for transactions to occur).

Conversely, it's possible to conceive of a better medium by which value can be transferred (imagine bitcoin with blocks generated every few seconds - fast enough to generate confirms that compete with credit card authorizations).

Other cryptocurrencies will gain popularity that offer superior options to bitcoin eventually, although this might take a while.  Buffett's dead on about bitcoin, but I definitely see other cryptocurrencies existing in the future and being quite popular.  Bitcoin's inability to compete with the instantaneous confirmation speed of cash, or the 5 second confirmation speed of credit cards, will render it obsolete eventually, fiat or not, it's just a terrible general currency platform.