Quark's policy is to support the three most current versions of QuarkXPress. So currently that is QuarkXPress 10, QuarkXPress 2015 and QuarkXPress 2016.
Yesterday we have introduced QuarkXPress 2017, which is scheduled to be released in 2nd quarter of this year, so release in April, May or June.
This means once version 2017 has been released we will stop supporting QuarkXPress 10, as then QuarkXPress 2015, 2016 and 2017 are the three most current versions.
To give you enough time to plan we have set a date for end-of-life for QuarkXPress 10:
We will end-of-life QuarkXPress 10 on July 31, 2017.
Of course that does NOT mean that QuarkXPress 10 will stop running on this date; don't worry:
QuarkXPress 10 will continue to run and you can continue to use it without any restriction; as it does not have a timebomb or any other restriction. It solely means that after this date you will not get any support by Quark for version 10 anymore.