I wanted to bring in a Feature Request to invite to client users as well, not just to dedicated meeting rooms or VMRs.
Right now it is not possible to invita guests to a User belonging to a Person, even though they have a conference system attached to their account. It would make sense that a User has the ability to invite people to join every video conferencing system and right now that's not possible.
Right now one has to change every invitation from his own Cloud-ID to the one from the endpoint associated user. This would probably save a huge amount of time of every assistant.