The Boeing perspective (previous ppt presentation link) includes a discounting of friction testing equipment results when the runway has more than 2.5cm of Snow. hmmm.....
The Airbus 'Getting to Grips' series on cold weather guide indicates a distrust of the friction measurement results as well. (The French translation gives this one some 'spunkiness in the read' - I give it - -
- )
I fully expect the NTSB to find more within the data-rich FDR secrets than the already known late reverser deployment.
Perhaps as already mentioned here, newly-formed ice at the moment of landing will become a factor - couple this with what looked like an increased groundspeed just before flare and touchdown - perhaps an added tailwind gust - neither would have been good considering the margins that existed on 31C at the time.