Note: mix of facts and opinions ahead; the facts mostly boil down to "all of these technologies _are_ used within Google"; the opinions are my own thoughts on what our internal future looks like. Other Googlers may see a different future or different reasons for the status quo :)

We do use gRPC internally, but the bulk of services were built prior to its existence/maturity and use its predecessors. My expectation is that services will eventually migrate, but that's a long way out. I'd say it's less to do with performance than a clear reason for teams to migrate, and several compelling reasons not to (yet).

Bazel is mostly a subset of Blaze, and many packages would "just work" if pulled into a Bazel workspace. Those that wouldn't are mostly broken because they rely on proprietary (but in many cases deprecated) Blaze features. I see a handful of changes go by every week migrating packages to newer Bazel-friendly definitions (a big one here is the historical handling of proto_library rules).

Kubernetes is used for some things built on GCP, but that's mostly suitable for green-field work (it's easier to integrate with existing things on Borg if you just run on Borg).