The 28-70mm focal length is more useful on full frame than crop sensors, as 28mm is quite wide and adequate for most situations. Many people do not like variable aperture zoom lenses, especially in the film days, but with digital it just makes no difference at all.
As I use the A7 more, I find that some of my lenses that were simply unsatisfactory on crop sensor bodies work like a new lens. The Leica-R 28mm f2.8 Elmarit is one, and this one surprises me as well. I don't regret getting rid of the Canon 5D Mark II and got the A7 at all. In fact, the A7 has become one of my favourite cameras.
Crane - Sony A7 & Contax 28-70mm f3.5-4.5 at f8