We are in a golden age for X-ray light sources, with thousands of scientists routinely using X-ray beams at modern synchrotron facilities to answer fundamental questions in chemistry, physics, materials science, and biology. The recent development of X-ray lasers has initiated in a new era in X-ray science by providing coherent ultrafast X-ray pulses with unprecedented peak brightness. The first generation of these facilities (e.g. the FLASH facility at DESY Hamburg, and the LCLS facility at SLAC) have already had tremendous scientific impact, and numerous similar facilities are now in operation or are under constructions around the world. However, despite their enormous peak brightness, the average X-ray brightness from these facilities is quite modest, comparable to or lower than that available from existing storage rings. This restricts their application in many important areas of science. This results from the fact that first-generation XFELs are based almost exclusively on pulsed-RF accelerator technology, which limits the achievable repetition rate. A new generation of XFELs is now under development that will overcome this restriction by exploiting continuous-wave RF superconducting accelerator technology (CW-SCRF) to provide ultrafast X-ray pulses at high repetition rate (~MHz) in a uniform or programmable time structure. This development is driven by important new science opportunities that have been identified and advanced over the past decade through scientific workshops, both in the U.S. and around the world. Most recently, a series of science workshops hel Show Partial Abstract