> It will take effort to prove that you indeed do have one or more of the "finite" (21 million is a big finite when it comes to collectibles) bitcoins.

Is it really? Here's how you can verify wallet ownership in about 10 minutes:

- The one who like you to verify the ownership generates a signature file from whatever they want

- Ask the owner of the wallet to add the hash of that file to OP_RETURN in a transaction from their wallet

- Wait for the transaction to be validated (longest step)

- The one who wants to verify the ownership can now compare the latest transaction from the wallet to the hash of their signature file

Same process applies for proving ownership of bank accounts, although if done in the weekend/evening, verifying the bank account will take longer time and you need to have a receiving bank account to read the signature hash, otherwise the process is mostly identical.

The rest of your comment is based on that you can't prove you own any bitcoins, hence worthless as you can prove you own bitcoins, it's trivial really. A quick search before thinking out loud would have shown you the answer.