The reality is most of the sites are already using virtual currencies..! not reddit already use Reddit gold, apple just launched there Apple Pay.. Google wallet.. etc etc. I do realize what you are saying but its gonna be pointless for them to do so because I don't think its gonna add any value to the brand unless they launch a decentralized sys and that's not possible with any of them.
The whole point of pseudonymity will be lost using these currencies. I just hate it when I have to sign in with my microsoft/google/facebook/yahoo account for some unrelated services. For this reason, I will not these other virtual currencies. I am sure that there are a lot of people who think like me