Due to their extremely low wing loading, powered paragliders stall at very low indicated airspeeds compared to other airplanes. A typical paraglider can continue flying all the way down to 10-15 knots.
That suggests the idea of using a fabric wing for flight at very high altitudes. At 100,000 feet, for example, an IAS of 10 knots corresponds to a TAS of 85 knots, well below the speed of sound. Suppose that we take a power source that works at low air density – say, a solar-powered electric motor or an engine with an onboard oxidizer tank – and attach it to a paraglider. Would anything prevent such an aircraft from flying stably at 100,000 ft? For example, would flutter be an issue?