According to latest rumors, along with upcoming Canon full frame mirrorless cameras, Canon will also announce new 50mm lenses after Photokina 2018.
The first rumored lens is EF 50mm f/1.4L IS USM lens, it will be smaller and lightweight and would suit both DSLRs and mirrorless cameras. According to previous rumors, Canon full frame mirrorless cameras may use native EF mount lenses. So this lens will fit nicely with such a release.
The second rumored lens is EF 50mm f/1.2L II USM lens, as there are working prototypes out there.