Apathy. When people take this system, that has been carefully maintained and built over decades (if you count the preceding cypherpunk era) for granted, then I think it becomes brittle and ultimately weak.

I've never liked the "digital gold" analogy for this reason. "Gold" is a rock that for some reason people value, but you never have to think about it. Bitcoin, if anything, is more like a democratic political system with a constitution defined by cryptography. And like any democracy, the second people become apathetic and take it for granted, I think it's a downhill road from there.

Specifically I'd like to see large institutional holders invest more in the long term success of the network, or at least publicly advocate for what they believe.