UIRepeat and UIData do pretty much the same: iterate over a collection of items. There should be a common base class for this, encapsulating the complicated logic for saving/restoring and iterating the state of the "rows". Something like "UIIterate".
Writing iterating components is very complicated at the moment. This base class should be easy to extend and also support any kind of data structures, not only "lists". Using an integer for the "row" iterating index is insufficient for creating "tree" components. A string or kind of indexing object would be much more flexible.
UIRepeat and UIData could extend this class and provide the existing interface on top of it.