UHD discs will be a niche product for several reasons. First is the expense of the players, screens and the movies themselves. This alone pushes the format into a luxury item for the time being, and for the next couple of years at the very least.
Secondly, the jump in visual quality is probably not enough in itself to excite the public into buying into yet another physical format. People seem to be satisfied with the "HD" they are getting now over cable, and it is nowhere near the visual quality of regular Blu-ray, much less UHD.
And third, the public wants convenience, and handling physical media, and waiting for the optical drive to spin up is becoming archaic. Not to mention the fact that you'll have to wait for the disc to be verified the first time you play it. DRM placed on the UHD discs is going to be an annoyance, along with the unskippable ads and previews.
And finally, for the tiny minority of folks who like to rip and change formats and play movies from hard drives in their media streaming boxes, the UHD discs will probably be untouchable for some time to come...years perhaps, before anyone breaks the encryption sufficiently well to consider using them as source files.