As above, there is little operational practicability in SVR, and even if calculated by crew observation there is no guarantee that this relates to a ‘true’ value of ‘visibility’.
Of greater benefit is a report first contact height during the approach and relating that to DH, but even so such information should be used with caution. Fog ‘thickness’ can vary with altitude as well as 'type', and thus what one crew saw another may not, or even what is seen at DH can be lost at lower altitude.
When on the ground, an estimate of RVR can be made against the number runway lights seen vs their spacing, but whatever is assessed should not be passed on as RVR as this has a specific meaning. There may be alleviations for this when lined up for take-off.