Under the global User management page (i.e. https://company.atlassian.net/admin/users) I'd like certain non-admin users (specifically: project leaders) to be able to add users to/remove users from specific user groups (in this case, their project's user group) but without being a global administrator.

Also see: https://answers.atlassian.com/questions/32522721/answers/32522788
A similar feature request for Bitbucket: https://bitbucket.org/site/master/issues/12062/allow-certain-non-admin-bitbucket-users-to