A particular thing I'm missing is to share read access to private repos with a link. Could be useful to share work with people that doesn't have a GitHub account (managers, etc)
We had a similar issue – we wanted non-product people to be able to view milestones, issues, report issues, etc and the solution suggested was to create a separate repository for issues.
This feature is not as big as all the other ones, but it's a nice improvement.