I was hoping for this functionality as part of the ‘links in custom fields’ work, especially as it aligns with so many of the ‘track projects in a project’ type suggestions and requests.
Would also make it easier to track who did what. For example, custom fields for who reviewed or performed each stage of a task. Particularly useful in a software development flow, at least until a ‘Person’ type custom field comes along.
I think I’m looking for the same thing I’d love to be able to add a Custom Field for, say, Subject Matter Expert that allows me to perform a lookup of a user, similar to how the default “Assignee” field works.