Originally Posted by PBL
1) The task was to consider a warning system which would remind the pilots to reduce thrust to idle on flare. But this is not necessary: there is one already.
Have cordially to disagree with that, PBL; and therefore with much of the rest of your anaysis. The task is (not 'was') to ensure that pilots correctly identify their problem as a wrongly-positioned TL (however caused); at the earliest possible moment in the landing process, not just in the flare.
From the CVRs, the Taipei pilots thought that they had a brake problem; the Congonhas ones thought they had a spoiler malfunction. Had either crew known the true cause, even after touchdown, they could have retarded the offending lever straight away (or cut the engine if the cause was, for example, a jammed lever).
As the Taiwanese investigators pointed out, the present 'Retard' call cuts out after touchdown, whether or not both levers have been retarded. That is clearly an inadequate arrangement, if not an actively-misleading one (given that after the present warning cuts out, the pilots will arguably, on the face of it, be even LESS likely to suspect a wrongly-positioned lever?).