Allow only custom fields in project scope to be shown in field config linked to the project

Currently JIRA will display all custom fields in the instance in each field configuration.
This leads to a lot of overhead for customers having many custom fields.
It would be better to show only custom fields within the scope of the project + with global scope (or give the customer the option to see all field or fields within project scope) once the field configuration is lined to a project.
This should improve usability for customer with many custom fields.