Interesting that there is argument about what BIM is. It's an acronym that spells out the definition quite clearly.
B - Building. BIM is specific to buildings (and the design, engineering, and construction of them.) AutoCAD and SketchUp are generic, which means they can be used for drafting, architecture, as well as other things.
I - Information. This is the critical difference. BIM models contain information related to the parts of a building. It maps the building data onto the building components. This is useful for scheduling, quantities, analysis, and yes, coordination. This is why BIM needs to be building-specific. AutoCAD and Sketchup alone do not do this as their core software usage, however, both have software "add-ons" that do some of these things, like AutoCAD Architecture.
M - Model. Meaning 3D modeling. Not a unique feature. As mentioned, SketchUp is 3D and AutoCAD has 3D capabilities. Although the fact Revit can produce a good 3D model as well as CD's is nice.
The information aspect (and by extension coordination) is the critical part. It is the information mapping, information coordination, information analysis, information scheduling that truly differentiates BIM from CAD. AutoCAD is arguably a more versatile drafting program (especially for those using it for 20 years). SketchUp is a breeze to model things.
So, to answer your original question, AutoCAD and SketchUp will go away when the use of BIM and it's embedded data unquestionably outweighs CAD's one-way process. When enough firms use Revit or Revit-compatible software that coordination without BIM is cumbersome. When engineers fully utilize Revit analysis tools and it's easier to link Revit models than export to another program. When architects and contractors begin to see that BIM quantity take-offs are easier than other methods. As more people use Revit and the software becomes more robust, the less CAD and SketchUp will be appealing.
