Airspeed determination
Failures in airspeed measurements seem to be increasingly implicated in aircraft upsets.
Rather than relying on pitot-based airspeed measurement, a number of contributors have suggested GPS-based approaches (which are unsuitable, as discussed).
As a back-up, could a fuselage-embedded mini-RAT type system work - an air-driven impeller (probably rather smaller than the cooling fan in your PC)?
Or perhaps even an acoustic system: a simple hull-mounted microphone which detects airspeed-derived noise? Frequency tuning or filtering could avoid interference from engine-derived noise.