The writing has been on the wall for a while. iTunes 12 already requires at least Windows 7, and a first-run Apple TV is very limited in what it can do (you aren't about to watch YouTube or stream Apple Music). However, this is the surest sign yet that Apple wants those with older devices to get with the times. While you're probably using something considerably newer if you're reading this, the cutoff might help you nudge a friend who's still clinging to an ancient PC.