Toyota hasn't exactly had a difficult time selling the Prius. The problem with this is that many of the experts believe we may be nearing the end of the era of hybrid/EV hype. That means trendiness alone won't be able to move Prii (Toyota's new official plural for Prius) and Toyota will have to offer a bit more practicality. At least, that's what they plan to do in Europe. The US will be getting the new Prius V, which has been improved but is still basically the same car.
Europe, on the other hand, will be getting the all-new Prius+, a Prius-based MPV with seating for seven. This means the Prius should be able to stay competitive in the face of the diesel-powered MPVs from other manufactures that can now achieve the same or better mileage. Of course, since the Prius doesn't have to compete with diesel in the US, we won't get one.