After the lukewarm reception to the Surface Duo series of devices, it seems that Microsoft may be considering a new form factor, namely one with three displays instead of two. The patent for such a design has been discovered in U.S. Patent and Trademark Office (USPTO) documentation, which gives us an early look at the purported hardware.
The patent, filed in June 23, 2020, was originally discovered by Patently Apple. Although the document is quite lengthy and somewhat technical, the image included in it (seen above) speaks a thousand words. It's essentially very similar to the Surface Duo, and just adds one more display.
That said, it does deviate from the Surface Duo in one significant way. As noted by Windows Central, the hinges are designed and positioned in such a way that when the device is collapsed or folded, it can expose a single display at all times. In contrast, when the Duo is reverse-folded, it exposes both displays. While you can fold it towards yourself, that exposes none of the displays. So when it comes to display panels, you can have either all or nothing when it using the Surface Duo. The patented design remedies this "issue".
The patent obviously doesn't describe the device as a "Surface Trio", and instead just refers to it as a "multi-panel display device". An excerpt from the document reads:
Multi-panel display devices may be useful in a variety of different scenarios. For example, multiple software application windows may be visually presented on separate display panels at the same time. Multi-panel display devices may use a hinge to allow for the display panels to fold in different directions (e.g., inward/outwards). Such foldability allows multi-panel display devices to have a larger total display area relative to a similarly-portable single display device, while also allowing for smaller folded dimensions relative to a non-folding display device offering the same display area.
With that being said, it is important to note that this is still just a patent for now. While Microsoft may be tinkering with some hardware internally, it's also possible that it's something that it has shelved for the time being. Furthermore, little is known about how the software - likely Android - would be customized to cater to three displays instead of two. We'll likely learn more about the hardware and the software in the coming months if the Surface Trio actually is in development, but for now, it's better to keep your expectations in check.