Given exponential scaling, it will not be long before chips with hundreds of cores are standard. For OS designers, this new trend in architectures provides a new opportunity to explore different research directions in scaling operating systems. The primary question facing OS designers over the next ten years will be: What is the correct design of OS services that will scale up to hundreds or thousands of cores, and adapt to the unprecedented variability in demand of the system resources? A fundamental research challenge addressed in this paper is to identify some characteristics of such a scalable OS service for next multicore and cloud computing chips. We argue that the OS services have to deploy elastic techniques to adapt to this variability at runtime. In this paper, we advocate for elastic OS service, illustrate their feasibility and effectiveness in meeting the variable demands through providing elastic technologies for OS services in the fos operating system. We furthermore showcase a prototype elastic file system service fos and illustrate its effectiveness in meeting variable demands.