Not thinking about the value of it, but of its future usefulness as value store and as mean of payment
I don't believe you can separate the value of Bitcoin and it's usefulness because the more valuable Bitcoin is, the more useful it becomes.
The more people who hold Bitcoin, the more scarce it becomes and therefore the more valuable it becomes. In 20 years, Bitcoin could go to 0, or become a widely used currency and skyrocket in value.
Once the number of Bitcoin holders reaches equilibrium then the value would remain stable, but we are definitely not at that point yet.
For the simple reason that it exist in the physical space and can't disappear, unless the laws that regulate our existence change, which is quite improbable
Gold will also work and retain a value even if society suddenly shuts down and reset to a "sticks and stones" state
Bitcoin advocates have this weird tendency to completely ignore decades of game theory
That's why people don't trust them