Guard has the nice side effect of turning an optional into a non-optional, so that you can use a value through a whole method without having to unwrap (or worse, force unwrap) it.
without requiring the code-by-convention Disposable implementation
Frankly that sounds a lot clunkier to me than just having a nice defer block.
"repeat/while" is retarded and an unnecessary change away from well-known and accepted language conventions.
I don't know how long you've been programming but over the years I have run across times where I wanted to run through a loop at least once before checking the end condition, and had to contort a variety of things to accommodate a check at the top of the loop... I hardly think such a useful tool is retarded, when is serves so well in a specific niche.
Protocol extensions are nice, and are probably going to be quite useful in keeping your code readable. C# has had extension methods for a while now
They aren't really the same as extension methods you are talking about, because protocol extensions allow for default implementations that get overridden... both Swift and ObjC have had extensions on classes forever.
Swift protocol extensions are more like C# Abstract Classes. But you can have a class declare conformance to multiple protocols and so gain all of the methods from each, and furthermore you can in an extension on a class make any class implement a protocol and thus gain default protocol implementations...