[sjs1234]

That specific premise is false. An alternate use case does not provide a -meaningful- floor for any store of value. Tulips still have an alternate use case.

I'd claim Krugman is arguing against cryptocurrency in general rather than Bitcoin specifically.

The affordances provided cryptocurrency are new. It's a fair bet that will provide value.

How many factors currently contributing to the value of the US dollar were in place within the first decade of its existence?

I'd also claim the libertarian hopes for cryptocurrency are overblown, though they are definitely contributing to its current level interest.