I don't think 2 languages are needed. Swift already rules iOS and (in my subjective opinion) Android (www.scade.io).
As someone who uses both languages almost every day, they're not as similar as it might appear at first glance.
Though they both have modern, cleaner syntax than their predecessors, they also are designed with very different requirements for integration. Regardless of those constraints, they solve similar problems in much different ways.
e.g. the fundamental rule in kotlin of everything being an expression, and the prevalence of Protocols in Swift.