The main goal was try and introduce these APIs to designers, since there seems to be a current of interest around designers getting excited about learning Swift.
I've had some feedback that I've made a bit of a mess with casting when trying to calculate a random number - would appreciate any best practices or thoughts on that...
This just feels like more proof that Swift will be nominally better than ObjC for the next 5 years, until Apple's APIs are (re?)written to make use of reasonable Swift idioms.
Also, this is the community's periodic reminder that not all ObjC (and soon Swift) is iOS; people still write (and use! imagine that!) OS X apps.
You brought up a couple of neat concepts that I wasn't aware of, especially "UISystemAnimation.Delete".