Not a bad marketing idea, but I think they are becoming a bit mainstream. There is Ethereum that is already considered the silver version of cryptocurrencies (in case we consider bitcoin as the golden version), and also Litecoin, that is considered being the little brother of bitcoin because of its similarities. Now we have the small sister. In the future I am expecting to have

bitcoin's nephew,
bitcoin's cousin,
bitcoin's schoolmate,
bitcoin's roommate,
bitcoin's European lover,
bitcoin's American lover,
bitcoin's Latin host,
bitcoin's best friend from Australia,
bitcoin's Indian neighbor,

and so on...