Unfortunately, the hardware of the device is still a mystery, but trains are often used by network engineers to test the cellular capabilities of a device. Still, it's an indication that this is a real device we'll be able to hold this year. In fact, Windows Central's Zac Bowden says he's hearing rumblings that the device may launch earlier than expected.
Either way, it looks like this version of the Surface Duo has a flash on its right-hand screen. That suggests the device has evolved somewhat since Microsoft's October 2019 Surface event, where there was definitely nothing there.
This could also mean we're looking at a single-camera setup for the Duo, but it may be that Microsoft is trying to increase flexibility. A camera on the front means users can access it while the screen is folded around, while the back camera offers (likely higher quality) options when it's open. Still, it's not much effort to simply fold the screen, so we'll have to wait and see.
The Surface Duo was previously spotted in the hands of CEO Satya Nadella, who was showing it off to Yahoo Finance's Brian Sozzi. However, we only got a slight glimpse of the screen from that angle, with the right-hand screen hidden.
Developers are already beginning to play around with the app ideas due to Microsoft's official emulator. It released an SDK for macOS and PC a couple of weeks ago to get the ball rolling for dual-screen support on Android.
I have little doubt we'll hear more about developing for the device at Build 2020 in May. When exactly it will release is anyone's guess with the circling rumors, but it would definitely be strange if Microsoft didn't utilize its Surface 2020 event in some form.