Personnaly, you can only see the limits of 1080p picture in extremely large screens at a decent viewing distance. So unless you have an image wall with a touch surface, acting as a multipurpose display for your home (a la Microsoft Surface), in short : the final evolution of TV+computer+domotic+other, more than 1080p is not viable commercialy, as is the SACD for mass market.
If 4K is just for movies, like SACD for music, the market will be very small, a niche videophile market.
4K screens could be used for 3D viewing without special glasses with a lenticular system in order to create a great "more than 1080p" 3D picture, but that's another story!