I've been doing some research on design choices in online communities, and I'm looking for some examples of design changes, events, feature additions (or subtractions), or policy changes that might have had an exogenous effect on user behavior on SO?
I realize a similar question was asked about three years ago: What events/policy changes etc. in SO have exogenously manipulated things like views, answers, votes etc.?
I'm looking for either updated examples, or possibly even things that were changed more than once.
Just for a bit of context, one example of the types of changes I'm looking for comes from the previously linked post: In June of 2009, low rep users (>500) were shown a "Please consider commenting" message after down voting a post or comment. I'm interested in seeing if that message actually had an effect on user behaviors.
Similar examples would be greatly appreciated. Thanks.