I haven't seen any speculation about whether the low energy state was even recoverable from the point where it was detected. Or to put it another way; given the aircraft is at the correct speed and position at 500' (notwithstanding that the Thrust Levers were at Idle), how long is the window for detection before the situation is unrecoverable?
A few points to consider:
-It is not clear from the data available when the recovery was commenced and what technique was used (eg the TOGA switch may have been pushed sometime after recovery was attempted).
-Speed may have continued to decay after initial thrust correction.
-Recovery from at or near stick shaker involves significant altitude lost. Speed must be recovered before attempting pitch up to avoid a secondary stall.
I think the window could be as short as 15 seconds. I could be completely wrong; I bet by now many people have replicated the situation in a proper 777 simulator. How did it go?