How can we improve WHMCS?

As a user I find Billable Items a clunky way of dealing with custom billing situations. Additionally I'd like to see billable items included in all income reports.

My proposal for an alternative is via recurring invoices.
When you create a manual invoice, you should simply have the option to make it a recurring invoice.
Set the recurring period
billing start date
termination date or continue forever
Contract period (to allow for minimum contracts, so cannot be cancelled before this date)

plus you already have the functionality built into invoices, to add payments, refund, notes etc.

This would be so much better than billable items.