This capability is currently available with Ultra Recall by copying or moving Info Items from one .urd file to another. You can either copy/cut and paste, or drag and drop from the source Info Database to the destination Info Database (.urd file) to split or merge .urd files. See this
topic in the online help file for the details.
We do have adding this same functionality as import/export wizard options on our todo list, but this change would only be an added convenience since it is already available via the above method. As you mentioned, this would be a use for a filtered Data Explorer pane, as discussed in other forum threads.