I find a common problem with theming and styling frameworks is that they try to do too much. If you agree, you might find CostumeKit by Jake Marsh interesting. Instead of trying to cope with everything, it's little more than a set of protocols which make defining, and applying themes easy.
I love a good post about API naming and this is a great example from Soroush Khanlou. He talks about delegate methods and proposes a different approach in Swift than we have in Objective-C. I like the idea.
Talking of component based UI frameworks, this is brand new from Spotify. The framework itself is written in Objective-C but it supports Swift (the demo app is Swift, for example). I haven't had a chance to give it more than a glance yet as I only found it about 20 minutes before sending this, but it's probably worth a look!