This is great, and I can't see it being controversial seeing as we've been talking about doing it forever ...
I assume this is for 5.1, since we've feature-freezed 5.0, eh?
Your TIP should probably make that clear.
I agree that being able to support the standard nav designs out of the box is a good thing, and it would be good to include a few sample themes for folks to build on. That would go a long ways towards making the toolkit more usable out-of-the-box, as has Lars's work on the default index page and other things.
