But to me the main problem was having built an iOS style environment, completely locked down, with no way to install anything unless you pay money to microsoft through the windows store (and redevelop your app). There was no technical reason to prevent regular .net apps from running directly on windows RT.
So it was a subpar experience compared to iOS without the power and flexibility of windows.
Lumia and Surface 1 and 2 were #2.
2. Xbox 360
3. Windows Phone 7 (on leftover chunks of Windows CE) on ARM
4. Windows Phone 8/Windows RT
5. Windows 10 on ARM
So, by my count, this might be iteration 6? (Though maybe more like 5 Part 2.)
Of course, the software is a mess, because nobody has bothered to build versions for RT in years, and none of the regular x86/x64 Windows software is compatible with RT.