This paper considers the rigorous design of Systems of Systems (SoS), i.e. systems composed of a series of heterogeneous components whose number evolves with time. Such components coalize to accomplish functions that they could not achieve alone. Examples of SoS includes (among many others) almost any application of the Internet of things such as smart cities or airport management system. Dynamical evolution of SoS makes it impossible to design an appropriate solution beforehand. Consequently, existing approaches build on an iterative process that takes its evolution into account. A key challenge in this process is the ability to reason and analyze a given view of the SoS, i.e. verifying a series of goals on a fixed number of SoS constituents, and use the results to eventually predict its evolution. To address this challenge, we propose a methodology and a tool-chain supporting continuous validation of SoS behavior against formal requirements, based on a scalable formal verification technique known as Statistical Model Checking (SMC). SMC quantifies how close the current view is from achieving a given mission. We integrate SMC with existing industrial practice, by addressing both methodological and technological issues. Our contribution is summarized as follows: (1) a methodology for continuous and scalable validation of SoS formal requirements; (2) a natural-language based formal specification language able to express complex SoS requirements; (3) adoption of widely used industry standards for simulation and heterogeneous systems integration (FMI and UPDM); (4) development of a robust SMC toolchain integrated with system design tools used in practice. We illustrate the application of our SMC tool-chain and the obtained results on a case study.