Many-core architectures trade single-thread performance for a larger number of cores. Scalable throughput can be attained only by a high degree of parallelism, minimized synchronization. Whilst this is achievable for many applications, the operating system still introduces bottlenecks through non-local sharing, synchronization,, message passing. A particular challenge for highly dynamic applications, for example invasive HPC applications, elastic compute clouds, is the management of short-living application threads, processes. This paper discusses OS architecture choices based on microkernel, multikernel, distributed systems designs, our development experience in the context of the MyThOS project. Initial experiments show a much faster thread creation, activation compared to monolithic systems like Linux while providing a more flexible protection, threading model that is better suited for dynamic scenarios. However, despite significant progress in the overall domain of operating systems, the design space for scalable many-core operating systems is yet to be fully explored.