I have just completed creating a patchset for slicer that builds against ITKv4 (from a few days ago), and is NOT using the ITKv3 compatibility options.
This patchset adds a new cmake option: Slicer_BUILD_WITH_ITKv4:BOOL=[ON|OFF] with the default setting to off. When ITKv4 is set to ON, SimpleITK is also built, but it is currently NOT integrated very well into the slicer environment.
I then built both the ITKv3 and the ITKv4 versions from the one common source tree.
In both build scenarios, the following tests failed in both cases (and only the following cases).
The following tests FAILED: 96 - vtkMRMLSceneTest2_helixGlyphs.mrml (Failed) 97 - vtkMRMLSceneTest2_helix_roi_tract.mrml (Failed) 100 - vtkMRMLSceneTest2_name.mrml (Failed) 101 - vtkMRMLSceneTest2_SlicePipeline.mrml (Failed) 103 - vtkMRMLSceneTest2_vol_and_cube_camera.mrml (Failed) 104 - vtkMRMLSceneTest2_vol_and_cube.mrml (Failed) 105 - vtkMRMLSceneTest2_vol.mrml (Failed) 106 - vtkMRMLSceneTest2_volRender.mrml (Failed) 107 - vtkMRMLSceneTest2_volScene.mrml (Failed) 174 - vtkDataIOManagerLogicTest1 (Failed) 228 - qSlicerAnnotationsModuleTest1 (Failed) 236 - qSlicerDiffusionTensorVolumeDisplayWidgetTest1 (Failed) 245 - qSlicerVolumeRenderingModuleTest1 (Failed) 246 - qSlicerVolumeRenderingModuleWidgetTest1 (Failed) 247 - qSlicerVolumeRenderingModuleWidgetTest2 (Failed) Errors while running CTest