Predicates currently take a client.Object and return a bool. With generics, we might be able to have typed generics, which would let ppl avoid a type assertion inside their predicate when they want to access anything other than metadata.

We currently type to client.Object, but this is both too much in the case of a source.Channel that could take literally everything that might not actually be a client.Object and too little in the case of everything else, as we lose the type information.