Features I'd like to see:
-Night-time drop with programmable time settings for each channel, instead of the single photocell style of the GCS.
-Ability to heat or cool as required to maintain temp. setpoint (2 relays required)
-Submersible temp. probes (already available commercially)
-Audible alarm which can be disabled, and flashing LED alarm
-Data logging capability
-Humidity control as an option
-Light control as an option
-Ideally, multiple relays which are assignable to a function, i.e. 8 relays which could be used for 8 heat controls, or 4 heat and 4 light circuits, or 4 heat, 2 light, and 2 humidity
That's all I can think of right now. I'm no electronics genius, but I do have extensive experience with similar control systems for commercial swimming pool chemical feeds. I might be able to help you out a bit if you need it.