As electric companies decarbonize, the path to net-zero CO2 can present challenges for electric system performance due to changes in the capabilities and operating profiles of both supply- and demand-side resources. This study utilizes a commercial modeling tool to analyze potential capacity portfolio buildouts and to explore associated operability challenges and opportunities. Capacity expansion planning and grid operations simulation models are implemented on an Arizona electric power test system. Results highlight the importance of flexible dispatchable technologies in ensuring operability in systems with high levels of variable renewable energy and fewer dispatchable resources. The study also underscores the critical role of negative emissions technologies in offsetting residual emissions from dispatchable technologies essential for ensuring operability.