The upcoming Canon full frame mirrorless cameras will be officially announced after Photokina 2018. According to latest rumors, new 50mm lenses will be also announced along with Canon full frame mirrorless cameras.
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.