Think of the SAFE network as a large single brain, there may be others with their own safecoin, but they will not interoperate at the network level, but maybe humans will interoperate to transfer cash between them (as with any currency/forex type thing). They will also not share data with the current design as both will require payment form the other to store and it will mean too many copies really. However if the network became a true network of networks then it gets very interesting indeed, but imagine explaining that one to folk 
This will all get interesting after this one is up and running of course 