Alexander Cornwell (Adds details, quotes, context) DUBAI, Jan 13 (Reuters) - Emirates Airline President Tim Clark on Wednesday said Boeing Co’s 777X might not enter into service with airlines until 2023 or even later, amid uncertainty over the development timeline of Boeing’s biggest twin-engine jet and when it will be certified. Boeing has been developing the widebody jet, a new version of its popular 777 aircraft, with the goal of releasing it in 2022, already two years later than planned. The 777X will be the first major jet to be certified since software flaws in two Boeing 737 MAX planes caused fatal crashes and prompted accusations of cozy relations between the company and the U.S. Federal Aviation Administration (FAA).