For me, Roon still wins out.
The Plex music library is awful for anything that does not follow the “Artist/Album” structure. And good luck with multiple values for fields like Artist and Album Artist. Plex has no support for the Composer field either.
I have discovered more about my own library with Roon’s metadata enrichment than I would ever have discovered with Plex.
The Plex sync feature is nice, but it only syncs to mp3… blech. If it had the option for syncing the original file, it would be better, but the music library is still a deal breaker for me.
As for Plex lossless FLAC streaming, that is nice. But in my testing on IOS, streaming a 192k 24 bit track to my Dragonfly Red showed that it was playing at 44.1k… The same setup with wifi streaming with the Roon app maxed out the Dragon Fly red at 96k.
So while this is an interesting development that I will be keeping an eye on, Roon is still my preferred player…