As computational infrastructure extends to the edge, it will increasingly offer the same fine-grained resource provisioning mechanisms used in large-scale cloud datacenters, and advances in low-latency, wireless networking technology will allow service providers to blur the distinction between local and remote resources for commodity computing. From the users' perspectives, their devices will no longer have fixed computational power, but rather will appear to have flexible computational capabilities that vary subject to the shared, disaggregated edge resources available in their physical proximity. System software will transparently leverage these ephemeral resources to provide a better end-user experience. We discuss key systems challenges to enabling such tightly-coupled, disaggregated, and ephemeral infrastructure provisioning, advocate for more research in the area, and outline possible paths forward.