I just watched one of my clients with an expired card and hosting account have a horribly confusing experience. First, the language could use an edit... the checkout screen shows the option to use an existing card by updating the expiration date. That works, but I think the section below should say "OR checkout with a NEW card" so that its more clear.
The biggest problem is that there was no redirect that the payment was processed... after entering credit card details the page refreshed with the same checkout form. (In fact, when I check the history log it looks like he paid twice.)
Hope this can be tested and worked out soon. Support Access enabled. Site ID#88 if someone can check.