Dude, I have some genius off-shoot non-BR games that Fortnite could make. It has my creative juices flowing. They should and will focus on BR as long as it's this popular, but I almost want to send them the ideas I have for the future.
Fortnite BR is still somewhat casual, but I think they could make a separate mode or game that draws in an even bigger audience and truly dominate the market. And it could be a nice break from frustration that can ensue in BR. Usually I just play a totally different game and comeback, but imagine how much they benefit if they can still keep you in their game.
They do have Save The World, and I believe they are making it free and it's probably fun, I've never played it. But they could aim bigger. I have about 5 ideas and one that is very ambitious. But if they made another game that has really never been done before, it would do so incredibly well. They have the whole world's eyes on them right now. Now, they don't need to necessarily, they will do more than fine with BR alone. But there is a huge opportunity to innovate gaming on another level.