Short trains and long platforms

I have written about this before but the subject came up in an article in the latest issue of Rail. Surely the solution is to fit all train doors with a simple detector in series with the locking system, so that they cannot be opened unless they are adjacent to a station platform? This would be simpler and more robust than GPS location, avoid the need to lengthen platforms, and could be retro-fitted to all stock, including, for example, mark 3 vehicles with slam doors and secondary locking.