The bad news is they briefly had one in Beta. it used a totally different distribution (IPTV) for its programming. A few people here even had it. Unfortunately they cancelled the Beta and decided not to do forward with the STB.
Not sure if the Non disclosure agreement still keeps those in the Beta from talking. I haven't heard any rumors of new UHD service.
ATSC 3.0, the new standard for broadcast, includes UHD and is in early trials in the U.S. It also is designed to include IPTV based cable. Anyone live in Phoenix? Once this becomes more available we MAY see something for FIOS.