We can talk about supporting the initial report, but can you point us to the JPA section that you think dictates that this should be supported? I do not think it says this.

The {{properties.put("javax.persistence.jtaDataSource", "");}}call should work. I have verified that it does work in 4.x but not in 5.x. Oddly what happens on 5.x is that the DS defined in the PU is used, but the EMF properties reports the overridden DS. This particular one should be fixed.