With regard to overwhelming the user's in-box.
I created this query that examines the number of messages a user might have seen if this functionality had existed.
avg | max | stdev
13.07 | 4,711 | 48.44
The average count of 13 doesn't seem to bad and the standard deviation of around 50 doesn't seem that bad either because the majority of users will receive less than 60. Based on my personal experience this would create about a 10% uptick in notifications.
There are some users of course that will receive a lot of notifications but these are people who ask a lot of questions, and given the amount of help they're getting it doesn't bother me a whole lot.