Ekkehard Gentz just showed me how to customize MagicDraw so that diagrams are really domain specific (no UML anymore). And it looks pretty cool. You can (and it seemed not to be too hard to do so) hide everything you don't want, extend and customize existing UML2 diagrams, etc.
In the end the modeling language ekkehard showed me didn't look like UML anymore. It was very simple and just showed the domain-specific concepts.
Unfortunately, if you go and process those models you are back in UML-hell again. But as all the customization information is modeled within the profile, one could transform a real domain-specific meta model (based on ecore of course) and a corresponing transformation from it. This would encapsulate the UML stuff completely.
Ekkehard will present his DSLs at this year's JAX during the DSL day.