Suggestion: That this "light patch" (aka "opto coupler") approach can help with STEM education. Maybe a setup where students can see the workings of the building blocks can help get them engaged?
Next step - a robot vehicle, the "Creative RAT".
Here a confession that this "Creative RAT" is not very creative. It repeats a 16 second sequence of forward, turning and reversing movements. That does sometimes make it appear to be relating to its enviroment - see the end of the video - but those are just coincidences, or the way that running through the cycle of movement will hit on something that works for the chair or table leg that it is stuck on. The name comes from "Creative Repurposing of Accessible Technologies".
Light patches are looking promising as an interface, They are easy to program compared to other interfaces. Control seems to be more precise than expected. This is working well on a low cost cellphone. Testing is good - we can get a lot of testing done with the phone alone without the need to run the robot or even have it handy. We can watch the light patches to see if the expected light-ups happen.
Programming note - follow-up to the posts here about which platform to use. I find that Xamarin has improved a lot with the release of "Microsoft Visual Studio 2017 Community". The Visual Studio install seems to include all components without the need for other supporting installs. We now have a primitive visual designer. I found this was good enough to prototype my UI, then looking at the markup code helped me get into fine tuning. Compile and run speed is a big improvement.