Will an independent crypto become a reserve currency in the next 100 years? My answer is I don't think so. But will a central bank put their currency on a blockchain? Yea I could see that, here is a story about the royal chinese mint

https://medium.com/@andrewkeys_88339/ethereum-growing-exponentially-in-china-31f1d24c8ee9

Could one of these central bank backed crypto's be a reserve currency? If they choose to, definitely.