Surely the logic could be programmed such that if Radio Alt =0 and/or Airspeed < say 120kts allow thrust over-ride.
And if the radalt fails? That then allows inadvertent TR deployment in-air. (if it's an OR gate).
The existing systems for determining the "on ground" state are intentionally complex in order to minimise the risk of inadvertent in-air deployment, even in the event of (possibly dormant) system failures. The hazard associated with in-air deployment is, for most types, severe. The hazard of failure to deploy on-ground is IN GENERAL small - because normal planning factors have sufficient margin to account for failure (or non-use) of reversers. Therefore the correct risk management approach is to bias the design to address the in-air problem, not the on-ground one.