The exact function is not specified so far. My _guess_ is that it could merely be the same virtual server-based Now Record Service function you already have from the old Now TV boxes, i.e. can be kept for 10 days only and are limited to specific channels.
Even after 1080p output became popular it toke some years for hardware to support 1080p (input) encoding to be viable in a consumer device.
Even 4K/60 is not universal in the latest output devices, so it will take a long time before a viable consumer-grade solution for 4K/60 real-time HEVC encoding shows up.