To meet the ambitious goals of next-generation 6G networks, including ultra-high data rates and ubiquitous coverage, we propose a novel high-altitude platform station (HAPS)-based integrated sensing and communication (ISAC) architecture. Operating in the stratosphere, the HAPS functions as both a powerful communication hub and an advanced environmental sensor. Combined with a fleet of cooperative uncrewed aerial vehicles (UAVs), this dual-purpose system forms a scalable and intelligent 3D network. Simulation results indicate that this approach significantly boosts network performance, improves sensing accuracy, and ensures a fairer service distribution across users, outperforming conventional UAV-only baselines. We conclude by outlining the prospective applications and a deployment roadmap for this technology for smart cities and other large-scale environments.