It's important to have clear goals, so our users and contributors know where we are going. However, teams like ours, made up of willing volunteers, are unlikely to follow a detailed plan closely and expertise in a topic is not always available.
Volunteers, though, are constantly surprising us. Someone new comes on board and, all of a sudden, we make great leaps forward in a neglected area. Sometimes a developer pairs with a domain expert to add realism to a crude feature and the pace of progress becomes amazing.
Our plans are kept on Launchpad.net, which also provides our bug tracking service. They are known as Milestones and there is more detail to be seen by clicking on each version up to the proposed Open Rails 4.0.
Please bear in mind that, in common with all volunteer projects, we cannot estimate or even guess at completion dates for any version.