I see 8k export is supported for image sequences and HEVC and it's working fine here. It also works for some AVI codecs like CineForm, Grass Valley HQX, MagicYUV and others, though not sure how much sense this would make.
Nice, that is one area of the marketing they could have been more clear... and I haven't had the chance to test it myself yet. The marketing states "8k file support by proxy", but that can confuse some into thinking it can only import 8k, but not render it. hopefully the 360 VR stuff got a resolution bump too...