I prefer to watch my video content from Plex Server + XPLAY (LG doesn't support 4k over DLNA, another stupid limitation) instead of Blu-ray player. I don't have a powerful computer to do transcoding, so when I buy a 4k blu-ray I simply remux it to mkv and add it to the Plex library - my files are very big, 50-60 GB per movie. Some of them have bitrate peaks which exceed 100mbps. My Plex box (linux) is capable of streaming higher bitrates, the TV itself is able to process these bitrates but is limited by the speed of the network adapter. The same movie would play without stuttering from USB3.0 (or even 2.0) external disk, but would stutter occasionally (>100mbps) when streamed from Plex library (using the same USB3.0 disk).
It would be very nice to have at least the option to install a gigabit dongle on the TV. I have already tried with Trendnet TU3-ETG but the TV won't recognize it. Maybe with a future firmware update it will be possible, who knows...