Hey Michal,
I thought your slides were great, and it truly illustrates the growing ability for us Ruby debs to be able to write common pieces of functionality that can be reused across multiple platforms. I think the biggest challenge will be to figure out the best way to architect an application not as a "Rails" app, but as an app with a reusable core that can be deployed via Opal, RubyMotion, and web server, along with the individual "expressions" of the app as a Rails app, an iOS app, etc.
Jared