I mean, the "irrelevance" scenario sounds quite depressing. But for me it's not quite the right word. Because the need for a hard decentralized currency isn't irrelevant. The right word for me is "ignorance". What if Bitcoin is relevant but people ignore it.

Let me tell you about the Ancient Greece Steam Engine (wikipedia):

Of course the steam enginewould have had "relevance" to ancient Greeks. But they didn't go through the first industrial revolution. It just didn't catch on.