I am in need of this very same functionality -- a way to show users that their subscriptions are ending.
I've only thought of two options to do this:
1 -- either adding a private calendar event for the person whose subscription is ending, as requested by voclain
or
2 -- adding a custom 'subscription expiration' field that is editable only by the admin but viewable to everyone
Is either of these possible?
Thank you,

Jennie