I am happy to inform you that starting with version 17.1.7, XAF Mobile (CTP) supports ImmediatePostDataAttribute. You can see how it works in action using our https://demos.devexpress.com/XAF/MainDemoMobile/ demo in the Payment object's View.
You are welcome to download the latest version and test this feature in scenarios you are interested in. As usual, your feedback is greatly appreciated. Do not hesitate to submit tickets in our Support Center.
NOTE: Automatic updates will not work for non-persistent calculated reference properties due to an OData specificity.