A few things that if possible would be nice to have with this:
-Cron job or something that will check users subscriber status and if they are no longer subscribed take them out of the specified group for subscribers.
-Display how many days left until users subscription runs out.
-Display how long the users has been subscribed for.
-Display other channels the user is subscribed to.
I would be willing of course to help fund this to be made if need be (I can't contribute a lot but would definitely do what I can to help get this made).
Why I think this would be a highly desired Add-on?
With the growing popularity of Twitch and the involvement a lot of Streamers of with their subscribers I can see this being something many people might want to look into having for their twitch communities.
Some resources that may or may not help: