Here's an update on your question, after speaking with the engineers:
3.0.0.4.374.5517 was released for RT-AC66U/ AC66R, RT-N66U/ N66R/ N66W, RT-N16, RT-N12HP, RT-N12 D1, RT-N10U/ N10U B1 a couple of weeks ago. .5517 had some stability issues on RT-AC68U / AC68R and RT-AC56U / AC56R, so for...