Crash bug caused project (asset db?) corruption, reimport all crashes editor

I've already filed two new bugs on this, 643510 and 643513, one for corrupted project and another for reimport all crash. But I was hoping someone here might have a solution to fix the problems.

I had my project from 4.6b21 working in 5.0b9, something caused the editor to crash. After that, every time I open the editor I get

Code (CSharp):

1. Recursive Serialization is not supported. You can't dereference a PPtr while loading. (Constructors of C# classes may not load objects either eg. EditorGUIUtility.TextContent should be moved to OnEnable. See stacktrace.)
2. UnityEditor.SpriteEditorWindow:.cctor()
3. UnityEditorInternal.InternalEditorUtility:LoadSerializedFileAndForget(String)
4. UnityEditor.WindowLayout:LoadWindowLayout(String, Boolean)
5.  
6.  
7. NullReferenceException: Object reference not set to an instance of an object
8. UnityEditor.EditorGUIUtility.Load (System.String filename, System.Type type) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:431)
9. UnityEditor.EditorGUIUtility.Load (System.String path) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:421)
10. UnityEditor.EditorGUIUtility.LoadGeneratedIconOrNormalIcon (System.String name) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:155)
11. UnityEditor.EditorGUIUtility.LoadIconForSkin (System.String name, Int32 skinIndex) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:178)
12. UnityEditor.EditorGUIUtility.TextContent (System.String name) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:75)
13. UnityEditor.SpriteEditorWindow..cctor ()
14. Rethrow as TypeInitializationException: An exception was thrown by the type initializer for UnityEditor.SpriteEditorWindow
15. UnityEditorInternal.InternalEditorUtility:LoadSerializedFileAndForget(String)
16. UnityEditor.WindowLayout:LoadWindowLayout(String, Boolean)
17.  
18. NullReferenceException: Object reference not set to an instance of an object
19. UnityEditor.EditorGUIUtility.Load (System.String filename, System.Type type) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:431)
20. UnityEditor.EditorGUIUtility.Load (System.String path) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:421)
21. UnityEditor.EditorGUIUtility.LoadGeneratedIconOrNormalIcon (System.String name) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:155)
22. UnityEditor.EditorGUIUtility.LoadIconForSkin (System.String name, Int32 skinIndex) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:178)
23. UnityEditor.EditorGUIUtility.TextContent (System.String name) (at C:/buildslave/unity/build/artifacts/EditorGenerated/EditorGUIUtility.cs:75)
24. UnityEditor.SpriteEditorWindow..cctor ()
25. Rethrow as TypeInitializationException: An exception was thrown by the type initializer for UnityEditor.SpriteEditorWindow
26. UnityEditorInternal.InternalEditorUtility:LoadSerializedFileAndForget(String)
27. UnityEditor.WindowLayout:LoadWindowLayout(String, Boolean)
28.  

I then tried to delete all assets in a backup copy version that had only an empty scene and NO assets. I still got those errors when starting unity. Then I tried deleting all library cache directories with no luck. A reimport all on the empty project worked. However, when I try that on the real project with 26k files / 4.5GB of data, it crashes the editor.

It appears to be a corrupted asset database, but I can't seem to rebuild. Anyone have advice here?