In multi project datasource there are typically project dedicated user groups or lists. Example Project Y Users, Project Y Admins, Project Z users and etc. Would be great if User List and Groups could be manages as project resources similar like Connected Projects does. Where you are limited to that Project WorkArea scope. Projects already has resource tab for workflows, environments, views perhaps should have User List and Groups there as well? 

One it would then allow Project Administrator to limit User list/ groups available for ACLs rather than list every list available. Mistakes are made and wrong user list / group are added to ACL due to similar project list naming unintentionally giving access to the wrong users.

Second it is considered security violation to be able to see what other Projects in datasource is and User Lists / Group names disclose that since Project indication details are typically in Lists and group names.

Third - this should also reflect in User Management tool in PWExplorer, since now every user in datasource can see what other users and their emails are in this datasource.