Microsoft has indicated that versions earlier the 1709 will last receive updates on April 10, 2018. Microsoft wants to have everyone using the same version of Windows so that security fixes as well as feature improvements are available to all users.
Windows 10 version 1511 is now at the end of the road so its prudent to upgrade to the free 1709 version immediately. Windows 10 1607 is also at the end of the road.
The next release expected in a few weeks is loaded with many new capabilities. It also has been hardened even more against the recently discovered CPU bugs.
While most users may not use all of the new features in Windows 10, the security fixes are the most important under the hood improvements.
Recent cumulative updates are essential to the security of Windows and we strongly recommend installing them immediately.
Microsoft has been hard-nosed about support deadlines, and for good reason. Once support ends, that is it. Run windows update and go for out for coffee.