Sony recently confessed they need to address the lack of telephoto prime lenses for the FE system. Something Nikon users have not to worry about: Today Nikon announced the 500mm f/4.0 ($10,300 here at Amazon) and the 600mm f/4.0 ($12,300 here at Amazon). What massive lenses! Of course it makes little sense to use them on your A7 camera. If you really need such a long focal length than jump on the Sony 500mm f/4.0 which is $2700 more expensive than the Nikon version but at least gives you full autofocus.
Let’s see if Sony will ever make such huge lenses for the FE system….