Directory Opus 12.10 will add support for a new type of viewer that comes with newer versions of Windows 10, enabling you to use the Mixed Reality Viewer in the preview pane for various types of 3D object files:
The objects can be rotated by dragging with the mouse, and zoom in and out using the mouse wheel.
Demo video on YouTube:
This update will be free to existing Opus 12 users. You'll need a recent version of Windows 10, else you won't have the Mixed Reality Viewer needed to display this type of file (unless you have an alternative compatible viewer installed).
The viewer should work automatically for these file types, provided you're using Opus 12.10 and a recent version of Windows 10. (I think the Windows 10 Creators Update should be enough, but have only tested with the later April 2018 "1803" update.)
Note that the viewer's capabilities are down to what the Mixed Reality Viewer component in Windows provides in the form of its viewer. What we're adding to Opus is the ability to work with this new type of viewer.