Development of dependable multi-/many-core systems requires assurance that the system is operable in a range of conditions, subjected to both functional and non-functional requirements. To achieve this, tools need to be implemented that can enable exploration of design options and be able to detect deficiencies earlier to avoid costly system re-design. In this work we discuss the challenges of design of multi-core realtime systems with timing assurance and discuss what are the requirements for modelling, testing and analysis tools. Digital Twin-based predictive modelling and fast design space evaluation are studied that work toward addressing these challenges.