If you already have a comfortable work flow, I would not encourage you to migrate just for the sake of it, but having the option to write a native app in Ruby is very compelling to a lot of people who might otherwise not be interested in writing a native mobile app.

RubyMotion supports xib files, storyboards, xcdatamodel files, and Android XML files (and localization files, etc), so if you ARE interested in switching, you don't have to stop using those if you're already used to them.