9.G, I believe that your first two sentences relate mainly to FAR operations.
The exact components of Operational Landing Distances (OLD) are not entirely clear, nor are the applications. There are indications of differences between Boeing and Airbus, FAA and EASA.
AFAIK there is no intent to change the basis of the certificated landing performance (manufacturer’s actual distances). Thus OLD is only an operational issue, but to add to the confusion Airbus also refers to an 'operationally’ factored OLD (FOLD !) which appears to use a 15% margin.
Furthermore Airbus hints of an undisclosed ‘factored’ equivalent of OLD which could be used for dispatch.
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As for reverse’: reverse thrust is not used to determine certificated landing distances unless the manufacturer can demonstrate a consistent high level of reliability – Midway and other accidents indicate why. The EU has a caveat for contaminated operations where reverse can be considered; the additional risk is mitigated by infrequent exposure to those operations. There are similar alleviations in AC121-195 for FAR wet runway operations with restrictions, but applications are few if any.
Whilst most operations use reverse, there is a tendency to rely on it, particularly in deteriorating conditions. Also, contaminated operations are increasingly being considered as ‘the norm’ without any other risk mitigation.