The irony is only LG currently manufacture large screen OLED panels.
These are what Panasonic, and now Phillips, buy directly from LG, and then stick their own badge on them, and inflate the price

They just change the framework for their own design, and in Panasonic's case they use an improved video processing board to get even better picture quality from the same panel.
I upgraded from a 55" LG 1080P OLED to the newer generation 65" 4K OLED. Both are fantastic build quality. the 55" had carbon fibre back panel casework, which is stronger and lighter than any thin metal and plastic frame.
So seen as though most modern Bluray players such as Oppo, have dual HDMI output, simply use one for extracting audio via the HD621/861. The other goes directly to the display. So no need for HD621 to support 4K. Of more use is whether the HD621 can support HDMI2 and the new Atmos/DTS X sound formats, and convert them to PCM. Sadly it cannot.