While other cryptocurrencies like Bitcoin and Ethereum can be sent through the Ripple network, they have to use a third-party counterparty gateway. Just like sidechains to Bitcoin, there will be counterparty risks. Think of it as an additional service that can be accommodated by Ripple but not necessarily. Whereas XRP being the native currency of Ripple will be primarily used by the banks, always. There exist no scenario where XRP is not used. Thanks for your support.