i go one step further, and put the domain layer behind a network interface (http or other) with a versioned API. IMO, trapping behavior inside a single application is just as bad as tying it to a framework. the domain layer needs to be available to the entire organization.

rails is just a tool to build a front-end app. i have many of those on my project. some rails, some sinatra. if they want to access shared behavior or data, they include the appropriate gem which knows how to access a particular API.