Shotcut now uses a clever way to embed consumer parameters in the project file, using a <consumer> tag. This way, all information is embedded inside the project file, and simply running "melt playlist.mlt" will render the project.
Currently in Kdenlive we call the kdenlive_render executable and pass all consumer parameters as arguments, and script rendering creates a playlist and a separate script containing the consumer parameters. We could simplify this, get rid of the "script" workflow, and simply have a "render queue" folder where we could store playlists with embedded consumer params for delayed renderings