A couple of potential issues,
1. Quality of the GPS sensors. If they're no better than the ones in smartphones then dedicated navigation devices will still have an edge. My Nuvi 765T is a pretty old device. My eTrex Legend HCx is even older. Both of them make my HTC Android smartphone's GPS sensor look like a child's toy. In fact the GPS sensor in my really really old Garmin iQue Palm OS device is just as good. (I know this because I'm using the iQue in my current travels because my wife is using the Nuvi. OSM maps have added new life to the old beasty!!)
2. Software quality. If the existing major players decide to take advantage of this and improve their products, we could win. But if we are left to the mercies of the "app store" developers trying to make a living on sub-$10 apps, we lose.