The release on the Shimano website (and this may be quoted in the other articles, most of which I haven't looked at) says this: "H-type handlebars are a new concept in cycling, designed to position the rider’s forearms in a natural position, mimicking the position of hands on the brake hoods of drop handlebars."

So basically, they're like drop bars without the drops. Honestly, that maps pretty well to the way I ride my bike 90% of the time. Of course, the other 10% of the time (generally fighting a head wind) I'd be really annoyed not to have another option. The wrist orientation is the main reason (by far) that I prefer drop bars over flat bars. The Metrea levers look like they could address the inferior leverage you get when braking from the hoods (as compared to braking from the drops or using flat bar brake levers). It's hard, especially for people with small hands, to produce a lot of hand force with your fingers as close to the brake lever's pivot as they are when your hands are on the hoods.

The prototype picture gives the impression that they will be just like bullhorns, but I think that's a case of marketing guys screwing up what the engineers are trying to achieve. The description reads like they are intended to have a much more upright orientation.