Cantabile 3516 and later can now reflect the current visible key range indicators as a sys-ex message.
For most people this will be of limited value because the sys-ex data format is exclusive to Cantabile, but if you’re building a custom keyboard (like @FantomXR is) then you should be able to fairly easily decode this in a microcontroller and setup a on-keyboard LED strip to show your key ranges.
To use it, create a binding from the Engine - Key Range Data binding source point:
The format of the generated sys-ex data is described here.
Note that in the above example I’ve set the manufacturer ID in the sysex data to 0x60 which according to this is “Reserved for Other Uses”.
This could be a fun weekend Arduino project
Associated Trello card here.