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, cause the HMD device to: implement a three-dimensional (3D) virtual viewport on the display, provide extensibility of the viewport to a 3D modeling application executing on a computing platform in the physical environment, the application supporting a 3D model that is rendered on a two-dimensional (2D) desktop on a monitor coupled to the computing platform, render the 3D model as a hologram in the viewport, and based on the head pose, enable user interaction with either the 3D model rendered on the desktop or the 3D model rendered in the viewport, wherein the 3D model on the 2D desktop on the monitor is independently rendered from the hologram in the viewport on the HMD device, such that the 3D model rendered on the 2D desktop and the 3D model rendered as the hologram are generated by separate components.