This means that Windows 10 will be the only platform supported by future CPUs like Intel's upcoming CPU codenamed 'Kaby Lake', Qualcomm's upcoming '8996' silicon, and AMD's upcoming 'Bristol Ridge' silicon. Furthermore, Microsoft will no longer update Windows 7/8.1 for Intel's 6th Gen. Core™ processor (aka 'Sky Lake').
Here's the rationale for the change from Microsoft:
Windows 7 was designed nearly 10 years ago before any x86/x64 SOCs existed. For Windows 7 to run on any modern silicon, device drivers and firmware need to emulate Windows 7’s expectations for interrupt processing, bus support, and power states- which is challenging for WiFi, graphics, security, and more. As partners make customizations to legacy device drivers, services, and firmware settings, customers are likely to see regressions with Windows 7 ongoing servicing.
For many users, upgrading to Windows 10 is free. You can check Microsoft's website for more information.