Ran across this Reddit thread last night.
https://www.reddit.com/r/ar15/s/nqzWtjzXd3
From what I can tell, it appears to be some kind of PVD coating that can be used to treat both the interior and exterior of rifle barrels. I've read rumors around the web that Sig may be using something like this on the 277 Fury barrels to deal with what should otherwise be quite the barrel burner.
PVD/DLC is a line-of-sight coating, thus hasn't been implemented for barrel bore treatment heretofore.
I thought "what the hell" (had a couple adult beverages last night) and messaged the OP.
He directed me to
https://rtcoating.com/ and said he handles sales.
Looks like they're based in Lititz, PA. About an hour and 20 from my AO.
I did tell him he should post here as you guys would definitely put his tech to the test.
Oh, btw, for those who aren't going to read the comments on Reddit (don't blame you), he's quoting $50 to treat barrels.
If something sounds too good to be true, it usually is, but again, this is interesting.