Assign Cases from sub-organizations to users from the Default Organization

[ar3diu]

I have noticed that when a case is created and an organization chosen, I can assign the case to users only from that specific organization. But, in an MSSP scenario I'd like to link the case to a customer sub-organization but at the same time, assign it to one of the MSSP Analyst Accounts created in the Default Organization.
Is this possible or isn't actually how the multi-tenancy is supposed to work?

[ar3diu]

I also noticed that when a user from the Default Organization creates a case starting from an event of a sub-organization and the Case Owner is left empty, upon creation the case will be auto-assigned to the user that created the case (even if he's part of the Default Organization). But later on, that case can only be re-assigned to users in that specific sub-organization and not to other users from the Default Organization