I too am concerned. We're living in a golden age of mainstream supers and fantasy, but I'm afraid it's a bubble that has to burst sometime.
That said, the state of superhero movies was covered on NPR's Marketplace a couple weeks back. The two biggest takeaways that I got from that are one, movie studios are owned by megacorps that don't understand or care about moviemaking, and two, that movies must do well globally in order to turn a profit, especially in China. Both of these forces contribute to an environment that supports low-risk, low-brow, big-budget action movies. This is good if you like superheroes or are Michael Bay, but the downside is that people have to get tired of supers sometime. That schedule I posted is pretty dense.