Adding a new head requires a new penetration to the wall from the outside. The Mitsubishi ductless system in the video has several slots where we can add new ductless heads to the home.

Bryan previously had just a fan cooling his attic (where his kids play and hang out), so he decided to add a ductless head for controlled air conditioning instead of mere ventilation. (Eventually, there will be a dehumidifier added to the attic as well) After the penetration is made from the outdoors, we mount the ductless air handler in the attic.

When using a multi-zone ductless system, you can have a slightly larger condenser than normal without fully loading the equipment with the total capacity. That way, you have wiggle room to add some expansions later.

Mitsubishi Cooling & Heating: https://www.mitsubishicomfort.com/