Mixed Reality (MR) headsets offer the promise of greatly enhancing the ways that archaeologists collect and interact with their data during fieldwork. Archaeology is inherently spatial, visual, and grounded in the 3D reality of the world, which makes immersive MR headsets a natural fit for our discipline. However, none of the existing MR headsets are suitable for continuous practical use during archaeological fieldwork. Therefore, we here undertake the important creative exercise of laying out a design for an ideal MR headset for archaeologists of the future. We base this design upon our own practical experiments with existing technology during our field excavation. First, we provide our motivation for pursuing this project, to enhance how archaeologists interact with their 3D data. We then present both a vision of how MR headsets could be used to support fieldwork, and we document the limitations of the current MR headsets that work against achieving this vision. Next, we present specific details for several different requirements for an ideal headset that could overcome these limitations. Our goal is to encourage other archaeologists to engage in experimentation with MR headsets during their own fieldwork in order to better understand the future possibilities. We also hope to encourage technologists and archaeologists to collaborate towards building new MR headsets that can achieve at least some aspects of our ideal design.