There isn't much of a threat IMO as even the industrial-grade supercomputers won't even be able to crack a private key off of a bitcoin address. Also keep in mind that there aren't any commercially-available supercomputer anywhere that can come near the level of quantum computing, or even quantum computing in itself is still an exclusive privilege to experience. Again, it will potentially take hundreds of years before we crack SHA-256, before going in to the juicy tidbits of bitcoin's algorithm. Perhaps by then, humanity would cease to exist because of reasons..