Rabbit Proto founder here, and I can give you some background elements about what led us to think that this particular concept was the best to get out there right now from a technology standpoint.

The project started actually looking at bringing a prototyping platform for Printed Electronics (let's call this PE). PE is huge both on the research side (printed microprocessors are happening since 2011) and the industry side. Chemical companies are massively investing in R&D for this as they see two things, a generalization of the use of this technology for massive production of touch panels & solar panels among for example as well as a continuing number of consumer electronic devices (high grossing applications) that take advantage of the unique properties of functional inks.

What we found very interesting and a potential game changer was the second application. We talked to dozens of people to confirm that this was actually a need and we started looking for existing solutions, and to our surprise there was not really anything out there at the time. So we started experimenting with 3D printing of plastics and silver filled silicone RTV in April 2012 and that was the beginning of what would become Rabbit Proto. Silver was great in terms of conductivity but super expensive and in the absence of a pick and place system we had to put components by hand inside our 3d printed objects and then lay down the trace. So we went through a reduction exercise and we realized that materials like conductive graphite paste could avoid the use of components if we limited ourself at first the printing of capacitive sensors. Our approach right now is to go to more complex 3D printed geometries (anatomically correct for example) with embedded sensing and interactivity using the conductive material. If new materials were to be found to be useful in the future, the syringe would allow users to be able to switch between multiple functional materials.

Lastly instead of designing a $100 000 machine, we chose the RepRap way and thought that progressively open-sourcing it would be a nice way to get the project a community of application developers and a good way to give back to the community that gave us the machines and electronics we are using.

Hope this helps, and we love feedback and suggestions!

Hopes this clarifies things!