China's Chang'e 4 lunar rover successfully lands on the far side of the moon, sending back important geological data (1) (launched December 7, will land January 3, 2019)
SpaceX's Falcon Heavy maiden flight is a success (aside from the central booster failing to land as planned)
SpaceX's Crew Dragon successfully completes its unmanned rendezvous with the ISS, but the manned flight is delayed to early 2019 (unamnned test flight delayed to Jan 7, 2019)
Boeing's CST-100 Starliner is delayed to early 2019 (rescheduled for March 2019)
Tesla fails to achieve its production target of 5000 Model 3 vehicles per week by March, but makes significant progress regardless (achieved 5000/week in early July)
The US Navy announces major funding cuts to its railgun program, as this program falls out of favour (funding was cut by $10 million, but China spooked us by installing a railgun prototype, so the program wasn't cancelled altogether).
Lockheed Martin's production target of 90 F-35 units is easily met (91 F-35s delivered as of December 20th)
Graphene consumer products become widespread (the only product I heard about were those graphene shoes; "widespread" will only happen once graphene is common in electronics)
Gene therapies continue to fall in cost, as treatments for disorders with more patients are developed. A therapy with over 10,000 eligible patients is developed, bringing treatment cost below $200,000/treatment (can't find data, but most likely false)
A team from a research university is able to reproduce Dias' and Silvera's metallic hydrogen results. The material is shown to not be meta-stable, disappearing as pressure is released (nobody has been able to replicate Dias and Silvera's results)
More interstellar asteroids are discovered
A woolly mammoth-elephant hybrid fetus is created.
US Democrats win majorities in both houses of Congress. Any major policies Trump has failed to enact by this point are dead in the water until at least the next presidential elections (won the House, but not the Senate)
North Korea's nuclear weapons program continues unabated; this leads to much friction, especially during the 2018 Pyeongchang Olympics. Armed conflict with North Korea in the form of a pre-emptive strike is officially ruled out by the Trump administration as it becomes clear that North Korea can accurately strike the US mainland with impunity (I had to split this up; the first part is true, but the last part is blatantly wrong).
Shinzo Abe wins Japan's LDP leadership vote. His push to revise Article 9 of Japan's constitution gains support as North Korea continues to test-launch ballistic missiles around Japan (no ballistic missile launches, but clearly Japan is moving to increase its military capabilities)
Putin easily wins the 2018 presidential elections in Russia, despite some concerns from the Kremlin (with 120% approval!)
Brexit begins to fall apart as documents on the projected costs to Britain are revealed to the public. Public opinion is now heavily against Brexit. It's not clear how Brexit can be stopped, but the incumbent Conservative minority government faces the prospect of a vote of no confidence (True for the most part, although support for Brexit is still widespread and strong in many areas)
A number of smaller NATO allies in Eastern Europe and the Baltics answer Trump's call to increase their defence expenditures to a minimum of 2% of GDP.
The US opens its embassy in Jerusalem, prompting a number of smaller countries to follow suit in hopes of gaining favour with the US. This leads to a period of violent clashes between Israelis and Palestinians in Jerusalem, as Palestinians announce a 4th Intifada (Guatemala and Paraguay followed suit)
Erdogan scraps the Turkey-EU migrant deal; southern EU nations are effectively left to deal with the crisis on their own.
Oasis are inducted into the 2019 Rock & Roll Hall of Fame (it's done the year before) (but Radiohead got it)
Germany wins the 2018 FIFA World Cup (not even Klose)
Lesson for 2019: max size for accurate predictions is one sentence.