They’re here! Time to give one a spin with Espruino.
How many I/Os are needed to drive electronic dice? – Tim’s Blog
https://cpldcpu.com/2015/05/24/plexingplus/
Just saw this on Hackaday, very nice technique for driving LEDs. I can’t believe we haven’t seen it before. It uses tricks with voltage drops to drive n²+2 LEDs with n pins, instead of the n²-2 that charlieplexing yields or the n of one-to-one connections.