A great feature that I'm sure many would love to see is to have the ability to use the supporter or pay to blog plugin to offer different levels of services.
For example: $10/ month for basic - $20/month for Pro - $30/month for Platinum
Network admins could select different plugins, themes, storage, mobile, ads etc. to come available to different levels.
Right now the supporter plugin only has one level, the pay to blog is all or nothing and the membership plugin only does front end 'content memberships'
What I'm thinking would be similar to what 37 signals and so many other companies out there do with their products but instead this would be focused on networks and blogging.