Despegue, the question is about the -800 not the jurassic park.
V1 can go below 100kts as stated,lowest vmcg by memory is about 93kts,for sure 99kts.
Common sense and experience with events like Air Berlin at Dortmund suggest that runway friction measurement is also an inexact science. Reducing margins on contaminated runways is not a good idea when you do not really know how much you have in hand.
Agree,therefore ATM not allowed but Derate ok if vmcg limited.