One thing to take into account is the complexity of the new device.
A chinese company can create a new tablet within 2 months, simply because all parts already exist: They buy a finished PCB design, an existing touch, a battery, etc. and slap it into a very simple case.
I learned that when I had to replace the touchscreen of a cheap chinese tablet: when looking for the part number, I found out it's a standard part that's used on hundreds of different tablets.
The touchscreen was complete with glass, frame and even clips where it's clipped together with the tablet.
So in that case, they simply slap everything together, which is a quick and easy task (the designs are tested to work, so not much debugging needed) and incredible cheap, as all parts are being produced in millions or billions of quantities.
The handhelds like the GPD XD are a bit more complex, as they add gaming controls, but it's still one simple case and probably only a minimally changed existing PCB layout.
Now, to create something like their Windows device, things get more complex.
The case is far more complex (not just a top and bottom), the PCB isn't a simple standard design anymore if you want to fit it into a case as small as Pandoras together with a keyboard.
And they'd need a design for Windows 10 - and I haven't seen many chinese Windows 10 devices yet.
So maybe they're waiting for a Windows10 PCB design they can buy and change it to their needs or they design it themselves, which will take quite a bit of time (a bare PCB takes 4 - 6 weeks to produce, so if they need to debug it and have different revisions, it adds costs and time).
Some companies in China where I asked for some stuff sent me finished handhelds which I could simply get from them with small design changes and my own branding
That's pretty common
Well, that's just based on my experience, don't blame me if they can slap up the device within a few months, but I personally doubt it and would be careful