I was using that jack to send X10 signals from an Arduino (although I've since retired that function of the Arduino - as I no longer need it).
I have designs for shields that fit the ZA-328 (Arduino UNO R3 born anew as a ZBasic device) and ZA-2560 (Arduino mega2560 R3 born anew as a ZBasic device). Both do true collision avoidance and can work with the TW523, PSCO5, XM10, Jeff's devices that emulate the TW523 and PowerLine Communications Interfaces of my own design (which isolate the controllers from the powerline).
They support low-cost WiFi and Bluetooth modules, have battery-backed RTCs and 128KB EEPROMs for timers/macros.
I also have a daughterboard which replaces the Cypress microcontroller in the CM15A. The daughterboard includes a WiFi module, battery-backed RTC and support for 128KB EEPROMs (on the main CM15A PCB).
I hope to have these available by July. All can be reprogrammed with the free version of ZBasic. Or one can reinstall the Arduino bootloaders (or just use Arduinos) if more comfortable in that programming environment.
I would be interested in a RaspberryPi-based control system - once that would directly connect via that jack (without the need for a CM15A controller), if anyone is working on something like that.
I do not have anything specific to the Pi but the latest version is supposed to be able to run a reduced version of Windows 10. Depending on what
reduced means I may be able to provide this. I plan to use GLBasic to create interfaces/apps for Windows, Linux, OSX, iOS, Android, etc. and it might be fairly simple to make a version for the new Pi.
Code for all the above will be
open sores so others can modify them anyway they desire.