Here is some additional information on the upcoming NiSi 250mm f/5.6 lens for E/R/EF/Z/F/GFX/XCD/X (previously reported here | the lens is based on the Minolta 250mm f/5.6 lens | NiSi lenses are sold at Amazon and B&H Photo):
NiSi to announce a new 250mm f/5.6 folding lens (E/R/EF/Z/F/GFX/X) and three cinema lenses