That is not possible. Not without changing huge amount code in unity. Fot example, theoretically activity-log-manager, hud, zeitgeist-datahub, unity-gtk3-module,bamf etc are not required for unity. But compiz and unity are written such a way that they would require those and without those unity will throw constant error or most likely will crash. For example
unity-lens-photos recommends shotwell, but if you click on photos without shotwell install it will write huge amount of warnings to journald. Its very difficult to resolve reverse dependency and circular dependency.
I am not going to provide a ubuntu-unity-core but rather ubuntu-unity-minimal package which will have hud, global menu, indicators, gedit, file-roller, terminal, screenshot, eog and few other packages installed. If Unity doesn’t crash I will gradually remove apps like Rhythmbox, Shotwell etc from the minimal binary.