I think it would make sense to show open only by default for 'ngit list'. So having an option to show all instead of an option to show only opened.
Discussion
Yes. Maybe a tabbed view which starts on the 'Open' tab and other statuses could be selected via left and right arrow keys.
More simplistically, it could just show open proposals and accessing proposals with other statues could be achieved by providing its nevent in a command line parameter.