AFAIK, the documentation isn’t the main problem. I’m pretty sure PS3 is quite well understood.
The problem is how to translate the code to a typical X86 architecture. PS3’s uses a very different architecture with a big focus on their own special way on doing parallelism. It’s not an easy translation, and it must be done at great speed.
The work on RPCS3 incredible, but it took them more than a decade of optimizations to get where they are now. Wii U emulation got figured out relatively quickly in comparison, even if it uses similar specs to PS3.