In this paper we examine why model-based user interface development languages and tools only have had a limited dissemination outside the research communities, and argue that there will be an increasing need for cross-platform user interface development in the future. To meet these needs, user interface development languages and tools must use new approaches. We examine some alternatives, and conclude that an approach based on pattern-based abstract compound user interface components as building blocks is the most promising. We describe this approach in some detail, and give an example showing how three quite different instantiations of one modelling pattern may be mapped to different running user interfaces using a number of mapping rules to two different implementation platforms with significant differences. Then we discuss what is needed for modelling languages and tools following the described approach to be successful and give some concluding remarks.