How can we improve WHMCS?

A useful feature, and which most hosting companies have, is the ability to tie a particular credit/debit card to a product. A client can have multiple cards on file and they wish to use a specific card for a specific service. Currently, WHMCS only supports tying PayPal to one product and, a card processor, but you cannot assign distinct cards for specific products - when invoicing, it uses the default payment method.

I, and I'm sure many other people as well, have clients who run various businesses, and the services they use with us are tied to different business cards. The only current option is to create multiple client accounts for them, which makes it more difficult for them and extra work for us to associate all of those accounts together so they can manage them by hopping around in the client area between accounts.

It should be made possible to assign different cards to different products/services so that when the product or service renews, it uses that assigned card.