I agree with you on how many different objects, such as seashells or even certain types of stones have been used as money by some cultures. However, the point of this article is about real returns, and the real return of Gold over centuries - for example - has been zero, and this is with it having aesthetic and intrinsic values. Hence, Gold is not an investment class that Vanguard supports. So, why would Bitcoin give a postive real return, whether as a wealth preserving asset or currency?
Vanguard can have whatever policy it wants to, it's a free country.
But I do think it's somewhat hypocritical of them to not have things like gold and bitcoin when they do give access to other currencies -- many who's fate is also ultimately dependent on political decisions and global social consensus.
It's one thing to say we're not going to be let people speculate -- it's also another to say we're not going to let people hold assets that can hedge against global turmoil or hyperinflationary periods.
In terms of returns, I agree -- bitcoin's supposed "return" doesn't come from a productive use case in the same sense as other forms of capital (at least not yet.. though it is increasingly being used as a productive form of collateral in many cases, much in the same way that gold used to be used in contracts). But if you believe there is a trend of net shift in consensus away from gold and towards bitcoin, then it's also easy to see why you might expect the price per unit of bitcoin to go up.
It seems weird to me that vanguard lets you a make a statement like "I believe in the US gov's solvency so I'm going to hold all my financial worth in a sweep fund that earns money off of short term gov debt", but then at the same time not say things like "I think there's a small chance that the US gov might f' it up, or the balance of economic powers might shift in the world and so I want to hold other consensus assets that might diversify outcomes in those scenarios".
