According to a Support article published by Apple, the Back to My Mac feature of macOS and iCloud is going away in this Autumn’s release of macOS Mojave. When the feature was first conceived it was designed to give you ‘easy’ access to files and folders stored on your Mac, no matter where it was. I suppose with the continued rise of cloud services and online file storage, the component isn’t as crucial as it once was.
I wonder how long it’ll stick about for older versions of macOS, as it does rely on some Apple service infrastructure on the backend. If Back to My Mac was something you relied upon, consider this as notice served.