My organization sells subscription services to enterprise customers, which is a different model from the consumer subscription model that Zoho Billing has been designed to support and I beleve this capability should be added. 

An enterprise subscription model is structured as follows. During the sales cycle, 2 things are defined. The term of the subscription and the billing frequency. For example, customer XYZ wants to purchase our service for 1 year and be billed monthly. At the end of the 1-year term we will contact the customer to see if they would like to continue to use our services, and if they do, we will perform a renewal for an additional term, in this example 1 year. During this renewal the price may increase or the amount of service they are purchasing may increase. 

Common terms are 
1 year, 3 years, 5 years.

Common billing frequencies are.
Up front, Monthly, Quarterly, Yearly (this allows the customer to qualify the purchase as an operational or capital expense).

The current implementation of Zoho Billing doesn't have any way to gracefully handle. This type of model to perform this type of renewal at the end of a contracted term. Adding this enterprise subscription model would greatly increase the customers that Zoho Billing would be able to support.