Rumor has it that Qatar has to block seats on its 283-seat Airbus A350-900 on the DFW-DOH run... looked into things, DFW-DOH is 7,932 miles.... A350-900 range looks to be 7,500 miles, so perhaps this rumor is true. I have no idea how many seats would be blocked though.
Boeing 777-300, which returns on the route December 1, has a range of up to 8,500 miles.