Multiple Universes, more fixtures. For our first setup, 24 will be fine, but for our event in May of next year, I expect that will not be sufficient. Also, controlling multiple universes is also important. Ethernet-based control surfaces, especially those that are application aware like those from Euphonix, are also important to me (I hope you will add them to Cuelux). As part of that, supporting motorized sliders would be great.
Finally, support for other kinds of control (joystick, track ball) where appropriate would be great.
I have only spent a small period playing with Cuelux, having not gotten my dongle yet.
I will let you know more once I have more experience with it.
/carmi