I recommend checking out Promises if you hate the messiness that comes with nested async operations. Similar to PromiseKit, Google's latest open-source framework helps simplify your code logic reasonably well. Not only does Promises feature 100% test coverage, but it also seems to perform a lot faster than related libraries.
After more than five years of mobile development, I'm still a fan of the MVC pattern & we use it in Polly. Although no design pattern is perfect, Pawel brings up some excellent points concerning MVC and shares a few tips on ways to prevent massive controllers from forming in the first place. Ultimately, my advice is to use what works best for you, regardless of what the hottest new trend is.
One of my favorite features of Swift is the level of flexibility you can achieve through extensions. With that said, too much flexibility can also be a bad thing. If you're feeling a bit adventurous though, I recommend checking out Tyrone Advit's detailed article on extending the