People who cared about BuddyBuild probably don't care much about Docker or "generic" CI services. There are plenty of those.

The thing about BuddyBuild was that it was "iOS Specific". You could point it at a repo and you would have your project building, signed and ready to install, in minutes. This was pretty unheard of. And still is. Trying to get iOS projects to build and sign on generic CI services like Travis, Circle or Drone means hours of pain to get it going and to keep it going. Been there done that.