I´d better waith for the A7S II. Or even just buy the A7r II. GH4´s 4K is not very good. And it´s low light capabilities are quite odd.
Definitely not very useful. Most of the times, the interviewed moves a lot from cut to cut and the tool can´t handle such a big head movement. In adition, you need the guy to be silent during the morph cut, which is not always possible.
Can´t wait to see what is capable to do the A7S mkII! Regarding the film, I´ve seen some shorts better exposed.