XDS is a gRPC-based protocol for pushing configs and updates. The data is represented by 'resource type' and 'resource names', and values are typically protocol buffers, but can be JSON or any other format.
K8S defines a similar API - based on Json, also defined as protocol buffers or OpenAPI schema.
XDS and K8S APIs are quite similar - and serve a similar purpose, to allow controllers and other apps to get real-time notifications when anything changes in the config database. K8S also supports 'update/delete' - which are not present in 'official' XDS, but relatively easy to extend or support as a separate gRPC method.
It is possible to write a one or 2 way bridge between the two protocols: it would allow a simpler model for watching K8S resources compared to 'list and watch', and likely provide better performance. On the opposite side, it would allow kubectl to be used to debug and interact with XDS servers.
In general, there are many similar protocols using GET/LIST and with some form of 'watch' or events - creating bridges to allow users to pick one client library and interact with different protocols seems better than current model of having one heavy client library for each protocol.