As a continuation of the incremental xDS theme, it would be good to provide a general ability for xDS servers to patch individual xDS resources. We have two use cases in mind:

• large endpoint lists in cluster load assignments;
• break-glass modifications applied to generic xDS responses;

The ability would require implementing an xDS-aware patch semantics in Envoy. This may need support from additional proto annotations to provide customizations to how lists and maps are combined (see https://github.com/kubernetes/community/blob/master/contributors/devel/sig-api-machinery/strategic-merge-patch.md, for example).

/cc @howardjohn @mandarjog