Good question. I have wondered this as well. If anyone knows of a good solution, please respond! I don't have much first hand experience with this, but here's my opinion anyway.
There are still other AJAXy goodness that doesn't fit into CRUD. Validations is an example. If you want to validate-as-they-type, then where will you put this? IMO this should go in a separate controller. For one you may need to share similar behavior across controllers, so moving it into a separate controller makes sense to me. You could move it into its own "validations" controller or just have a more generic "ajax" controller where you place these little things. I wouldn't bother trying to make this part RESTful.
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