Training on copyright data is arguably considered fair use in quite a few jurisdictions to various extents and levels of precedent, and entirely legal for entities based in Japan.
Still, for certain languages, only libgen and public piracy websites contain any scientific or fiction material in digital formats. E.g. my native language doesn't have easily accessible e-books at all, unless you go through illegal means.
I hope somebody undertakes the steps necessary to train on the entirety of libgen. The amount of high quality tokens in libgen should be substantial.