How to deal with multiple users working on one scene?

We have large scenes in our projects, with multiple developers working on the same scene, which is a nightmare when it comes to (svn) merging.
Is there a recommended solution how to deal with that issue? Obviously, the release of multi scene editing, which could have been a help, has been delayed (Multi Scene Editing | Unity Blog). There is still Application.LoadLevelAdditive, which could be abused to achieve something similar, but it would still be just a help, not a real solution.

But how do the thousands of unity developer teams all around the world deal with that issue? Or am I missing something obvious?

Thank you in advance!

@m.mayer I know this is an old question, but are you still looking for multi scene editing capabilities? We are working on a tool exactly for this that is in beta. Check out Pricing — KinematicSoup Technologies Inc.