When Microsoft formally revealed Windows 10 back in September 2014, the company stated that it would be the last version of Windows. At the time, it wasn't precisely clear if this implied that there would be no Windows 11.
From then we saw Microsoft introduce several new Windows 10 SKUs in 2015. There was Windows 10 S, which can just run Windows Store apps, in addition to Windows 10 Pro for workstations. These are simply different versions of Windows 10 for PC.
However that does not imply that Microsoft isn't really thinking about drastically simplifying how Windows 10 works, and eliminate all the legacy things that make the OS too complicated, too slow, and too battery starving. Android beat Windows as the dominant OS for Web usage in 2015, and Microsoft definitely will not let Windows 10 rest on the sidelines in the future.
In 2015, we found out that Microsoft was apparently working hard on making Windows 10 more modular, an effort that has actually been codenamed "Windows Core OS." This is an essential work for developing new form-factors powered by Windows, such as the foldable mobile device that we've already seen in numerous patents.
Windows Core OS might be the base of two new operating systems from Microsoft: Andromeda OS, which will apparently power the company's rumored foldable mobile device, and Polaris, a streamlined version of Windows 10 for PCs.
Compared to Windows 10 S, Polaris will apparently be more lightweight and modern, dropping the existing Windows Shell, the legacy Control Panel and more. Polaris will be developed completely on Microsoft's UWP technology, but Microsoft stated to be working on bringing support for legacy Win32 apps when needed.
Polaris will apparently exist side-by-side with standard Windows 10. Existing Windows users will not be able to upgrade or switch to Polaris, nor will eventual Polaris users be able to upgrade to standard Windows 10 Pro. Most likely, Polaris will be able to deliver far better battery life thanks to removal of all legacy features, and it should also be as simple to use as an iPad or a Chromebook.
Microsoft has actually already attempted several times to simplify Windows, beginning with Windows 8/RT and now Windows 10 S. Polaris will apparently be a new beginning that truly pushes Microsoft's UWP platform forward, but could it attract consumers?
The majority of people now associate Windows with a desktop OS that offers you total liberty: That's why lots of people still do not think about iPads or Chromebooks as real PCs.
With the increase of Chromebooks and mobile devices though, Microsoft may well not have the choice to not dramatically change how Windows works. Polaris may not appear until 2019, assuming Microsoft does not cancel it at some time.