Entity Coupling Service another name for Composable Data Service
For me it smells more and more like Astoria + "Aggregation" (not that Astoria doesn't plan to support composition or aggregation, this I am not sure of).
I noticed that in some comments to that post, Udi expresses his opposition. I am not sure he opposes the entity services Mats refer to, or the idea of aggregating multiple data sources. I wish he explained his stance in more detail. Mats explanation of Entity services makes me believe the refers to services that only handle a single kind of entity each, which to my intuition sounds like exaggeratedly granular.