Nothing official. I’ve looked at hdmi.org and various TV manufacturers web sites and nobody mentions it.
However, when the first eARC enabled equipment starting hitting the market there were several messages on LG, Samsung, etc sites asking “why can’t TV apps pass TrueHD & dts-HD MA audio?” with no good reason why not.
This is speculation on my part due to a lack of hard evidence. I’m guessing there is a licensing component involved. The TV manufacturers might have to license TrueHD from Dolby and dts-HD/dts:X from dts, Inc. They want to keep their costs as low as possible, so they do not license the tech.
Licensing costs are also probably why Apple, Roku, Amazon, etc do not add TrueHD capability to their devices. No streaming service supports TrueHD due to bandwidth requirements. The additional sales generated by Plex/Emby/etc users would not cover licensing costs to add TrueHD audio to all units sold, and Dolby may not let them license it as a per-device add-on capability.
I would love to be wrong on this. It seems silly to drop $1500+ USD on an OLED TV then have to drop another $200 USD on a Shield Pro to get TrueHD/TrueHD + Atmos audio. Besides the cost, I’ve another device I have to configure, maintain, etc.(and another remote to lose between the couch cushions 
).
I’ll tag @TeknoJunky to see if he has any more recent intel.
Here’s his good thread with additional details on Plex, 4K, and lossless audio: [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k
