1. A head mounted display (HMD) device operable by a user in a physical environment, comprising: one or more processors; a sensor package; a display configured for rendering a mixed reality environment to the user, a view position of the user for the rendered mixed-reality environment being variable depending at least in part on a pose of the user's head in the physical environment; and one or more memory devices storing computer-readable instructions which, when executed by the one or more processors, perform a method comprising the steps of: implementing a three-dimensional (3D) virtual viewport on the display, supporting extensibility to a 3D modeling application executing on a remote computing platform, the application supporting a 3D model, and rendering the 3D model as a hologram in the viewport.