This is fact, was reported by the Seattle Times recently. EK has some doubts that the current B777-300ER GE90s will be able to deliver enough thrust all over the year in DBX´s hot climate and waits for a beefed-up version before commiting to the B773ER.
DXB is for sure not the most friendly climate for any engine - and I assume that GE90-powered B777s will have some problems there, too. I remeber rumours that Saudia was having some problems with theirs but can´t proove it. I think it is something no engine willbe able to escape from.
RR and PW can develop a 115K-engine if they want - but won´t have an application for it. GE has an exclusive contract for the B777X - as RR has for the A340-500/600. Had negative impacts on both sides: Air France decided in favour of the B777-300ER because the A340-600 has RRs, Cathay and Singapore have said that they are far from happy that the GE90 is the exklusive engine on the B777X and that was a driver behind their A340NG decisions.