I've attached to this post an early version of a membership add-on that enables some form of integration with our supporter plugin. It should initially only be used on a test install until you've run through some test to make sure it's working as you expect on your system.
It functions as follows:
1. Individual subscriptions can be marked as being "Supporter Integrated" - those that are not marked as such will function in the same way as they currently do.
2. Marked subscriptions will, when a user is added / signs up to and progresses through the levels of, will update the supporter expiry date of the users site / blog based on the period length of the level they are moving to. This works with finite and serial levels, I still have to implement indefinite levels.
3. The blog / site that is extended is identified initially as the one marked as their primary_blog (wp_usermeta) for which they have an administrator role.
4. The blog / site to be extended can be overridden by selecting a new blog / site from the users profile / user_edit screen - the user can select the site themselves, or an admin user can do it.
To install the add-on, download the zip file attached to this post and uncompress it. FTP / copy the file to your membershipincludes/plugins directory.
Please do let me know any feedback on it's use and anything we can add to integrate the two plugins further.