Right after I returned all of my DVR/STB's they added DVR playback to the FIOS Mobile App. But never saw anything on Apple TV. They talked about this in a video years ago. And with the THIN STB they should do it.
But once I got my ATV 4 and Channels App I started using the HDHomeRun Prime(s) with CableCards which works really well and much cheaper. I was paying about $70+ per month for the boxes and DVR. The 2 CableCars are $$ per month each. However, there was a hiccup with the SD/Channels DVR so I am hoping to be back on track with it later this year.
BTW... Since switching to Frontier FIOS (they took over Version in my location) the FIOS Mobile App no longer works. They can not tell I am connected to WiFi for some reason. And I am sure the DVR is not working with them.