Flexible assessments are distinct from standard research-based assessments like the Force Concept Inventory in that the items and the item ordering may differ between administrations. Our group has been developing a flexible assessment for upper-level undergraduate quantum mechanics called the Quantum Physics Assessment (QuPA) to address the lack of consensus on what can/should be taught in an undergraduate quantum course. This assessment will exist on a web platform where instructors can select topics they want to assess and other testing parameters. In Fall 2023, we conducted 34 interviews with faculty from institutions across the U.S. asking them to interact with our flexible assessment instructor interface, as well as about their experience with assessments, what they would improve, and what feedback would be useful. This paper will present the theory and motivation for flexible assessment of quantum mechanics proficiency, discuss our interview protocol, and summarize the general views of the instructors.