Providing the ability to email stakeholders based on custom field values extends the usability of a custom field to the realm of messaging. There are many things that cannot be accomplished with the built-in fields and a custom field must be used. But the usefulness of that custom field diminishes when you cannot use it within a messaging task to email stakeholders.

For example, say you built a single-value QD field for Service. A Service will have one or many stakeholders assigned to it, which may need to be notified via messaging tasks when something is happening to that Service.

It would work the same as how stakeholders are currently exposed within the messaging task recipient selection. You would see Request No/<customfieldname>/Stakeholder. Stakeholders could then be selected from the Role dropdown.