I'm amused to see PBL try and put down HUM, who I happen to know personally. Believe me, or not as you wish, but he does know a thing or two after the career he's had/having.
As for the engine failure theory/feathered prop theory. I'm not sure why this still prevails in some people's minds. We now have 'what's next's' contribution and there are also previous contributions from those with Metroliner experience who have satisfactorily explained why this might occur. On top of that, the AAIU's carefully worded statement early on effectively ruled out engine failure.
I suspect that lack of control authority at lower speeds will feature heavily in the final report and as usual with accidents will be the final link in a chain of events.