Once again, Sony Computer Entertainment may have inadvertently leaked a release date a bit too early. Last night for a short period of time, the US PlayStation Store showed the release date for the new God of War as March 22, 2018. The site has since been corrected to the old placeholder date of December 31, 2018, but not before I took a screenshot.
Since the 2017 PlayStation Experience is coming up this weekend, it's likely that a release date announcement will happen for the new God of War. Given that, it's possible that someone jumped the gun in regards to putting the date up on the PlayStation Store.
Of course, it could be a straight up error and mean absolutely nothing. The last time this happened, it was the then-unannounced Yakuza Kiwami 2 appearing on the Taiwanese PlayStation Store. The game was officially announced a day later.
God of War is currently scheduled to come to PlayStation 4 in early 2018.