Limitate sharing for editors

It would be nice to have a way to limit the sharing capabilities. In our scenario, we create User-Groups which represent our Customers. Then we add the People of the Customer as Viewers to this Group. Each Cusomer has it's own Collection, so we Share the Collection with the Customer-Usergroup and give them Editor Rights to let them participat in our Protocolls and Specifications. If such a Customer user uses @-mentions or clicks on Share-> and searches for a User, they see all our Customer Groups as also all Customer-Users. So it would be nice, if we could limit some Users (for example the Editors and Viewers) so that they can only share or mention People to which the document also is shared to. As now we have a privacy issue, because we leak information of People of different Customers to each other and also the Information about our Customers. Problem Currently, when we share a collection with a customer-specific user group and grant them Editor rights (on the Col…