How can we improve WHMCS?

I would love to see an option to customize payment terms based on the customer. Some of our larger customers who take a long time to process payments would like to get their invoices sent to them far in advance (i.e. 60 days) versus other customers prefer to get their invoices closer to the due date (i.e. 7 days). The reason why setting everyone to a date further in advance is not a good option for us, is that many customers see a far off due date and ignore/forget about the invoice, so it's creating an unnecessary email far in advance for them.

Right now we just set all customers to a shorter date, and then enable "Don't Apply Late Fees" and "Don't Send Overdue Emails" in their profile. This works okay, but it confuses customers when they get an invoice with a due date they know they can't meet and then it sits in our overdue invoices page for several weeks.