Technical Farm showed off a number of different versions of this Flare Adapter at the show, including EF to E-Mount, PL to E-Mount, and an EF to EF teleconverter adapter. It's certainly an interesting idea if it ever comes to market — as Technical Farm was trying to gauge interest (though whether you could get it shipped to the US is another question).
Either way, it's a specialty adapter, but I'm of the opinion that flares tend to look a lot more realistic in-camera, especially those flares that you can get from lens whacking — which involves pulling the lens off the mount and holding it in front at different angles so light can leak in. This adapter essentially lets you lens whack without having to pull the lens off the camera, and you've got much more control over how it flares.
I would love to see an American company come out with something similar, as I could see a ton of use for this not necessarily in cinema, but in all sorts of creative videos where you need that little bit of something extra.