But the worry is as we've seen, Apple seems to be moving to a 5 year time limit on OS support for all its devices. After that you'll get a couple of security updates, maybe. A 4K Apple TV works perfectly fine now, but in 5 years? And what if they stop OS updates then and stop there own app support, so no Apple TV app on your Apple TV, and what if they force other apps to have to update which means they don't work on older OS versions, they do that now even, which stops those working on your OS version too.
All whilst your perfectly happy with your hardware which may still be working perfectly fine.
A lot of what if's and it will be interesting to see which path Apple follows here.