The article in question is a good example of spreading misinformation.
And therefore I think that is a real credible threat. Bitcoin is a public ledger; therefore, so you can go out and see the public keys which are holding the massive balances and you could go out and target the several hundreds or thousands of Bitcoin and say I’m going to spend my effort on the computing resource in order to reverse engineer the private key from the public key, which is exposed. I think that is even a near-term threat.
First of all, it is not true that the Bitcoin's public ledger contains public keys. It contains bitcoin addresses which are 160 bit hashes of public keys:
A Bitcoin address is a 160-bit hash of the public portion of a public/private ECDSA keypair.
source: https://en.bitcoin.it/wiki/Technical_background_of_version_1_Bitcoin_addressesUntil the bitcoins associated with these addresses are spent (by providing the corresponding signatures), you can't even know the public key, let alone the private one.
And even if you knew the public key, you would need immense computer power and who knows how many tens of thousands of years of using that computing power to deduce the private key.