I do this too! A big benefit is gradual migration - for example, if I'm injecting DataContext into a bunch of different places, I can implement part of the functionality of DataContext. Once I have just enough functionality implemented to support one of the places it's injected, I update that place to take DataContext2. Then I can test, and move on to the next place.

If you're using a language with strong typing and good refactoring support (right now that's C#/Visual Studio for me), the eventual rename from DataContext2 to DataContext is a non-event.