I think Dojo looks great. Their rich text editor demo looks like it's designed to plug in to the Django admin :)
Before we get too far into the "which Ajax framework should Django use" discussion, I think it's important to lay the groundwork first. It seems to me that the goal of any Ajax support in Django should be to make it easier to integrate with any Ajax framework. If there is a default Ajax framework coupled with Django (it may just be a matter of which one is bundled and documented) it should be at least as easy to use another framework (or frameworks) as it is to use other template systems. Loose coupling, sensible defaults, etc. So the real productive question at this stage isn't "which Ajax framework", it's "how can Django make Ajax easier for app developers." At that point, what framework you use or whether you roll your own is up to you.
