Real transactional volume is going to be on permissioned blockchains, all public ones will become heavily regulated and the rest is going to be used by darknet. This is the future like it or not. Few currencies is really enough. From my perspective even one is enough.  Businesses don't really want to duplicate infrastructure to support new currency.  People can pay with bitcoins and that is enough unless the network is going to go down completely the chances of which is quite slim.