Hello. I think this is a brilliant project and I thank Rory for exposing FarmBot as an open source project. I am a final year Electronics Engineering undergrad from Sri Lanka. My final year project is on an automatic aquaponics system that is scalable. The Farmbot can be used to strengthen the automation task. It is my opinion that for a scalable solution, provision for future expansion in software must be accounted especially in the early stages of development.Using a SCADA system in the early stages can benefit later on. OpenAPC is an open source Supervisory Control & Data Acquisition (SCADA) software that consists of an industry standard CNC router(Beam Construct package for laser scanning & marking )driver within the SCADA software package. This package has several software ports and is highly flexible. There is a great chance that the FarmBot will evolve into a system that consists of a multitude of sensors and actuators, and the developing software should be able to cope up with these demands. Also this allows interoperability and provides a standard software platform for the project. Just some Food for Thought. 
The link to openAPC is given below, cheers!!!
openapc link