Symmetric encryption is already resistant / immune to quantum computing attacks. The best they can do against symmetric algorithms is cut their key strength in half, giving 256 bit algorithms the still unbreakable key strength of 128 bits. It is only asymmetric algorithms that have a lot to worry about. I don't know when we will start to see implementations of multivariate quadratic polynomial algorithms, there are quite a few papers discussing how to implement them though. I think it will be quite a while even after people have the ability to break RSA/ECDH before they use this ability against the people here. I think the NSA will be the first agency with such capability. But as with everything, things tend to work their way downwards over enough time.