Add a new CustomField Type?

Is it easy to add a new CustomField Type?
I’d like to add a custom date field, but the closest I can get with standard
RT seems to be a “Enter one value” which translates to text only.

Steps includes

  • Add a new entry “Enter one date value” to $CustomFieldObj->TypeComposite.
    How is this done?
  • Add a new Elements/EditCustomFieldDate. How do I add all functionality for
    a date field? RT can handle smart values like ‘now’.
  • What else?

Is it a completely wrong way to get date validation for a custom type?