Update:

> IBM has opened the A2 core:
> https://github.com/openpower-cores/a2i
> https://git.openpowerfoundation.org/cores/a2i

New core contribution hinted at:

https://openpowerna2020.sched.com/event/eDtC/new-core-contribution

I have a hunch it will be the PPC405. After all, IBM already opened the core to researchers and academia through Power.org back in 2006.

http://web.archive.org/web/20120722083542/https://www.power.org/news/articles/405download/