AF447 should not be brought in because the crew was overwhelmed. They didn't see anything not even the pitch that resulted fro their actions forget the GPS GS. UAS procedure is based on a philosophy to manage the aircraft speed within a safe band, accuracy is not the purpose nor is it possible. It is similar in Boeing or Airbus. After having applied recommended procedure GPS GS may be referred for awareness but it won't be wise to fine tune anything. Airbus has come out with back up speed(different from B/U SS) obtained by applying lift equation to GW, AOA, CG. It's there in A350 and optionally available on other models. If fitted then it's as simple as AP/FD TCAS. You do nothing. Just Say thank you.