A KPI to consider if the level of social maturity has been achieved, where upon Social Monetization is a firm possibility and execution is warranted.

Monetization Pursuance Initiative (MPI)  = # of positive non branded posts/total net *100

The % is likely going to be more for non-regulated, than regulated. In either case no one size, fits all.

Such a KPI forecast and a watch is sure to alert you, that the goal post is in view. Keep a watch.

Update

Ernest Paul, Head of Social Media at Cigna developed the ‘Monetization Pursuance Index’ on the 24th of January a Key Performance Indicator index for Social Media.
This specific KPI allows commercial brands to determine if their social media engagement has achieved a level, in par with a level of Social Trust with the customer, and an environment for a monetary transaction exists.
The formula to calculate the Monetization Pursuance Index (MPI) is as follows:
Monetization Pursuance Index (MPI) = # of positive non branded posts/total net *100
There exists a greater likelihood for regulated industries to score lower. This should be considered quite normal. This is very much in line with the Net Promoter Score (NPS) for regulated industries.
The % is likely to be greater for non-regulated brands as social engagement and trust is developed early.
The ‘MPI’ index serves as a watchtower to alert the brand that the social monetization goal post is in view.