I'm keen on getting the Assest UPNP docker too. I'm also a licensed user. Currently using MiniDLNA but it's not as good as Asset as I prefer the Asset views especially for it's sorting into the letter of the alphabet which makes it quicker to drill down to the music you want and Asset is just for streaming music.
Asset is free to use for non commercial purposes with only the UPnP server function. The other features are all licensed - Internet Radio, Dynamic Playlists, Jukebox Random Selection, Browse by File & Folder, PC Sound Card streaming from Windows installs, Dynamic Browsing, DSD support and Assest Collections. The difference between free version and licensed is the binary.
I'll look into building a docker myself and see how I go.