Over the past couple of months, Epic Games has been discussing plans to allow players to merge progress across Fortnite accounts, meaning that you'll be able to transfer your Fortnite currency, items, and costumes from your PS4 game to another console, and vice versa. This functionality was meant to arrive before the end of December, but it seems it has been delayed at least a little while into early 2019.
At this time, no specific reason for the delay has been given, other than that they want to ensure technical issues are sorted before the feature launches.
"We want to make sure that this process is thoroughly tested and working properly before releasing it to those of you currently looking to transfer purchases from other accounts to your primary account. We'll be sure to update you as we get closer to the release of the feature, which will include a web page on launch to help guide you through the flow!"
This process, once available, will allow for players who created multiple Fortnite accounts to bring all their win and loss stats, as well as paid items, into a single account. We don't know exactly when next year it'll happen, but "early next year" suggests it shouldn't be too long of a wait.