One of the goals is to avoid the need for additional motors, servos etc. This clearly limits the implementation to the type of gantry and possible motions.

The CoreXY design has a very unique property, it allows unobstructed access to the area between both motors, making it the preferable place to keep unused hotends. Additionally the motion capabilities of the gantry can be used to lock/unlock hotends in/from their respective parking position. My current implementation reduces the build area by 40mm in Y and requires 60mm in X per hotend. Reworking a printer with a native build area of 300x300mm would result in a machine that can hold 5 hotends and leaves a 300x260mm build area.