Details about Iceborne are pretty sparse so far. Capcom posted a short teaser trailer for the release, which is almost a full year away. In it, you can see a dragon-like monster named Rathalos flying across the ocean before reaching a previously undiscovered island of rock and ice. The trailer fades out before too much is revealed but longtime Monster Hunters might recognize some audio and visual markers that appear at the end of the video, including a strong hint that the monster Nargacuga may appear in the expansion.
In addition to the Iceborne expansion planned toward the back half of 2019, Capcom is also planning on a Monster Hunter crossover with The Witcher 3 that will bring Geralt into the Monster Hunter universe. The There's no word on when that collaboration will become available, but it looks like 2019 is shaping up to be a good year for Monster Hunters.