As a result of the Opt-In RFC[1] and discussion in the RFC meeting earlier this month[2], I will be presenting a draft specification for the feature before the end of the new year.
Please see the meeting summary for an overview of what was agreed[3]. I will need (even if I don't remember to request it) some design help for this feature, so lots of comments are encouraged and desired.
[1] https://www.mediawiki.org/wiki/Requests_for_comment/Opt-in_site_registration... [2] http://tools.wmflabs.org/meetbot/wikimedia-office/2014/wikimedia-office.2014... [3] https://www.mediawiki.org/wiki/Architecture_meetings/RFC_review_2014-12-03#M...