OK, I'm trying to setup a consistent email experience and I'm finding an issue.

My need:  Days Remaining Until Renewal

I am setting up a 1 year renewal period.  In that case, it would be useful to the end-customer to know how many days are remaining rather than have them do the mental math.  There is no field available for this.  Would be great to see it as part of the data-set.  But I can think of many reasons why it is a bad idea to add this data element.  So I respectfully request.....

Alright, I get that a "subscription" is a special case of an invoice. But as such it retains all of the custom-fields that are created for Invoices in Books.  The custom fields are defined in the APIs too.  They can be modified from within the UI of the Subscription Module. They will show up in invoices as well.  Please make these available from within the email templates and I'll take care of the Days Remaining calculator.

Thanks!