What do you mean by “little movement on open-sourcing the firmware?” The EC firmware source is right here on their GitHub, and there’s a table of codename → product translations for each branch (original post here):
(Admittedly it is easy to read but hard to customize. I just wanted to change some PL1 TDP constants in the source code once and couldn’t even get to reproduce the default firmware for the FW12. The build system is so confusing, and I asked for help in multiple places months ago and got no help.)