I haven't used CRDs myself for a few years now (probably since 2021), but I still remember developing CRDs was an ugly and hairy experience to say the least, partly due to the flaws of Golang itself (e.g. no traits like in Rust, no macros, no enums, etc...). With protobuf you can easily compile your definitions to any language with clear enum, oneof implementations, you can use the standard protobuf libraries to do deepCopy, merge, etc... for you and you can also add basic validations in the protobuf definitions and so on. gRPC/protobuf will basically allow you to develop k8s controllers very easily in any language.
I never said that CRDs are tied to Golang, I said that the experience of compiling CRDs, back then gen-controller or whatever is being used these days, to Golang types was simply ugly partly due to the flaws of the language itself. What I mean is that gRPC can standardize the process of compiling both k8s own resource definitions as well as CRDs to make the process of developing k8s controllers in any language simply much easier. However this will probably complicate the logic of the API server trying to understand and decode the binary-based protobuf resource serialized representations compared to the current text-based JSON representations.
