MFS, #7 interesting.
The exception for LCY is probably based on the use of a 35ft threshold crossing height and steep approach glideslope. Also the old runway had a fixed distance marker along the runway to indicate ‘the last point of touchdown’. However, I do not know if this still applies with the extended runway, or how such a marker might be interpreted for the wide range of aircraft types now using the airport. Even so a fixed marker may not guarantee that the rollout distance to stop is within the remaining runway length, for the conditions.
Your interpretation of the requirement for a non-standard runway would require the crew to add the air distance to that available beyond the glideslope origin. This would provide an estimate of the landing distance available which could be compared with the distance required. However, the (allocated) air distance would still be an estimate, with no relationship with the certificated distance and little with actual distances unless specifically published.
I wonder how the operational regulatory authority might interpret the landing distance requirements vs the description (exemption?) in the airfield requirements.