Back in 2012, when Microsoft rolled out the first tablet part of the Surface lineup, the company also introduced a new operating system to power the device and start what it hoped to be a new trend that would attract several other partners already selling Windows PCs.
Windows RT, however, was used by Microsoft itself for only two devices, the original Surface and the Surface 2, before being more or less abandoned - this actually happened in September 2015, when the company rolled out a small update to bring a Start menu on Windows RT desktops too.
And even though everyone believes that Windows RT doesn’t have a place in Microsoft’s vision, it appears that the company is at least considering building a Windows 10 version that would run on ARM-based chips.
As mentioned by Petri, Windows 10 RT references have been spotted in the PC versions of Windows 10, and although no specifics are available at the moment, it’s believed to be an indication that Redmond is at least considering the possibility of bringing a new SKU of its operating system to the market. Seeing Windows RT mentioned in the policy editor is not confirmation that the OS exists, though, so don't take anything for granted for the moment.
Windows RT is an operating system that has never been successful, with large OEMs, including Samsung, refusing to build devices running it because of the imposed limitations. Windows RT works only with applications from the store, and given the lack of apps on Windows 8, not only did users avoid to buy a device running it but also manufacturers refused to create them.
As a result, the original Surface RT proved to be quite a flop, with Microsoft itself coming down to a $900 million (€850 million) write-down in order to adjust inventories because of unsold units. The Surface 2 was produced in lower figures, though, and Microsoft itself abandoned Windows RT for the third-generation Surface.