yeah like Gravity Forms on wordpress. Easily add "conditional", then shows all other custom fields and you can choose what you want to match, contains, start with, ends with, greater than, less than, etc.
Easily done by a programmer and can make the custom fields much better. In fact, somehow integrating a system like gravity forms as the custom fields system, would make this much better, but that is hard to do since that is for wordpress and this is for WHMCS. Just saying, it would make this way more powerful.