CHANGELOG.mdに記述がありますね。

### 2014-10-09 (Xcode 6.1) * Objective-C `init` and factory methods are now imported as failable initializers when they can return `nil`. In the absence of information about a potentially-`nil` result, an Objective-C `init` or factory method will be imported as `init!`.

今でもあるのかな？