It certainly does seem to be a "scheme" but I wonder how it compares to other fiat or gold currency when looked at through a "scheme" lens.

When does it stop being a fad?

There is. The Schemer is Satoshi Nakamoto and anyone else involved with bitcoin's initial creation. They stand to profit handily by selling off their coins at many times their original, minimal value. But unlike a ponzi scheme or pyramid scheme, one can't trace fraudulent transactions directly to the schemers. It doesn't mean that it not a scheme.

Bitcoin isn't just a fad, it was clearly designed to enrich the original founders and early adopters at the expense of whoever is left holding the bag when the bubble bursts.