This work examines the challenges and opportunities of Machine Learning (ML) for Monitoring and Operational Data Analytics (MODA) in the context of Quantitative Codesign of Supercomputers (QCS). MODA is employed to gain insights into the behavior of current High Performance Computing (HPC) systems to improve system efficiency, performance, and reliability (e.g. through optimizing cooling infrastructure, job scheduling, and application parameter tuning). In this work, we take the position that QCS in general, and MODA in particular, require close exchange with the ML community to realize the full potential of data-driven analysis for the benefit of existing and future HPC systems. This exchange will facilitate identifying the appropriate ML methods to gain insights into current HPC systems and to go beyond expert-based knowledge and rules of thumb.