Enable invoices for contributions with 'partially paid' status

Some work has been done in https://issues.civicrm.org/jira/browse/CRM-17815 to the contribution invoices, which are nice improvements.

My issue is that currently a contribution invoice (email or pdf) can only be created for contribution statuses 1) completed 2) in progress or 3) refunded

Is there a technical reason why we cannot create invoices for the status 'partially paid'. It seems this is by far the status that benefits most from letting the customer know how much he/she paid and how much is still due.

I wonder if this is an arbitrary change (e.g. allow the status partially paid), or if this needs major refaktoring of the underlying code.