I have heard from Istation Support Services. Here is what their response to my email on the XML Exchange for ECDS.
Our TEA Export will pull all fields of data required by the state of Texas in an XML format. Additionally, if a school does not have students unique ID numbers or birth dates, the report will not populate until the missing information is input into Istation and then the report can be rerun to pull the desired information in the XML format. Administrators or PEIMS coordinators having issues obtaining the report can call the support line at 1-866-883-7323, Option 2 and an agent can assist the user on the exporting process to ensure they are able to submit the report to the state of Texas.
This sounds very helpful. Hopefully ECDS submissions will go much smoother this year.