Samsung claims that it has conducted a series of consumer surveys and it is now confident that there will enough demand for a foldable smartphone, so it decided to move the launch of the galaxy X from early 2019, to late 2018. The real reason why Samsung is making this move is most likely that it does not want to allow Chinese OEMs like Huawei to get a head start in this emerging market.
https://www.notebookcheck.net/Samsung-confirms-arrival-of-the-Galaxy-X-foldable-phone-in-late-2018.328766.0.html