What you're saying is absolutely nothing new. There's a lot of FUD and confusion in this thread (no surprise) but this has been apparent from the very beginning. "A Proof of Stake Design Philosophy" [1] makes the essential nature of cryptoeconomics very clear. In short: (a) all currencies are social phenomena (b) all the fancy math does is replace the "men with guns" that protect physical currencies -- that is, currencies must be economically defensible and (c) what actually gives real-world currencies their value is the presence of a tax authority who creates the currency and then demands it back at some later point [2]. PoS creates an absolute demand for the currency; it is nothing more than a formalization of currency power.

> So, aside from being a geeky toy and new market for gambling, where has cryptocurrency actually succeeded?

A better question is -- why are there so many currencies to begin with? Why isn't there a single currency that everybody uses?

Once you understand the answer to this question the value of cryptocurrencies become clear. You said it yourself: currency is inherently a contextual and social value construct. Different communities have different values. Communities that develop currency power will always triumph over communities that don't because they can collaborate more effectively. Currencies don't "succeed," communities succeed -- and they do this partly by leveraging currency power. The answer to your question is right in front of you but you just don't want to see it: the cryptocurrency development communities themselves are already wildly successful and have demonstrated the ability to raise enormous funds and collaborate effectively.

[1] https://medium.com/@VitalikButerin/a-proof-of-stake-design-p...

[2] https://www.youtube.com/watch?v=boHE_dR159k