While what you say is true, it's also possible to arbitrarily declare another metal "the new gold" just like it's possible to make a new cryptocurrency.
No it is not possible. All the possible alternative metals are already known and traded commodities. Gold also has many properties that people find desirable in a store of value: it is stable (resistant to oxidation), relatively rare, workable (fairly soft), etc. A new hash is for the most part equivalent to the last in the ways that count.
