Feature Request: Make Membership levels, subscriptions etc sortable in admin area

I have a feature request for the membership plugin that would really help me to more efficiently perform member administration.

Currently in the All Members screen of Membership we can filter our member list by subscription, level etc. In additoin I'd like to be able to:
1) also filter by gateway
2) add an option to the "filter by" to include "none" as an option (instead of picking a level or subscription). Our site allows for partial signups and a number of current members don't have a subscription. I'd like to be able to quickly search for these people and there is currently no easy way to find them other than paging through the entire member list.

If its not possible to do the "filter by none" request above could the columns in the members list be made sortable? This would work like the fields in the native Wordpress User list that lets you sort by username, email etc. It'd be great to sort membership by level, subscription, gateway