In 4.01 CSD01 we have proposed that a nested collection within a delta payload can be represented either as a replacement of the collection (where omitted values are removed from the collection) or as a delta payload (where only enumerated values are changed, and removed entities are represented as tombstones).
The way we differentiate between these two is, in the case of a nested delta, by annotating the collection property with a context url specifying a delta:
"members": [ ... ]
Alternatively, we could just use a delta annotation prefixed with the property name, as in:
"members@delta": [ ... ]
Which wouldn't require using the contextUrl annotation to interpret the property.