Problem

Currently, it's possible to add People field on next-gen projects, but it's not possible to restrict who will appear on this list. 

Suggestion

Add the option "Configure" to the field, so we can use the "Edit user filtering" and add a group of people to show in the dropdown. This is the option we see on "User Picker (single user)" for system custom fields.

For JSD this option is great if we want to restrict customers to select their managers, for example, so they won't see other customers and users.