Intel is working on a model of the recently released Atom z7-8700-soc that will be able to playback video at 3840×2160 pixels with 60Hz, the current model will 'only' do 30 hz.
Video playback possible at extended screen through HDMI 2.0 The pending version of the Atom z7-8700-soc would use a little more power though. the 4-k display playback can be managed by embedded DP on the UHD screen of the product itself and then thus externally through HDMI 2.0. The one caveat, this will only apply to 4-k video in the h.264 format with a 200 to 250 Mbit/sec bitrate (encoded). The h.264-codec with 4K can only do 30 maximum.