References to Windows 10 Cloud began appearing in Insider Preview build 15019, but then it was reported that this new SKU of Windows would only run apps from the Store, similar to Windows RT. WindowsBlogItalia has now come across some screenshots of the OS, which are sure to bring back memories of Microsoft's failed RT attempts.
Surely, anyone with a Surface RT remembers what happens when attempting to install a Win32 app...
...and the message clearly states that the version of Windows is made to run Store apps only.
We can see another screenshot showing resizable Store apps, which is one thing that Windows RT lacked. In RT, all of the Store apps were fullscreen, despite it having a separate desktop environment, which was mainly used for the Office RT apps.
With Evernote open, we can see that this version is running Project Centennial apps, which are Win32 apps that have been converted for the Store. This would certainly work on x86-based machines, and likely higher end ARM PCs that support Windows 10 on ARM. It remains to be seen what the company's plan is for lower end ARM-based PCs.
The other thing that you'll notice here is that the watermark says that it's Windows 10 Pro build 15019. The report says that it confirmed the edition of Windows as Cloud via the Registry Editor.
It might be best to take this report with a healthy dose of skepticism. While these do fit in with everything that we think we know about Windows 10 Cloud, it's still not entirely clear why the watermark says Windows 10 Pro, as the Registry Editor is not proof beyond a reasonable doubt.