Channels in C# are just a regular library, it would be overkill to introduce syntax changes to the language just for this. Btw, you have other ways to get the producer-consumer pattern in .Net, Channels are just one of the various options but you also have BufferBlock from System.Threading.Tasks.Dataflow (with a more complicated API).
Prior to channels, we'd add a ConcurrentQueue<T> from System.Collections.Concurrent to the service then expose a public method that enqueued an instance of T. Controllers then received the singleton instance of the services through DI and would invoke that method to add a job item to the service's queue.
Obviously, that created a direct coupling. You could set up an interface and have the controller consume the interface instead, but it was still a coupling in practice. I suppose you register the public method as a delegate or something instead and just inject the delegate, but that's a bit hacky to me, and I think my juniors would find it confusing.
If you really wanted to you could create a simple Channel wrapper that operator overloads some visually arrow-like operator, exactly such as C++'s famous stream overloads using << and >> byte shift operators as "stream operators".
That sort of "cutesy" operator overloading is generally frowned upon in C# best practices, but still possible if you don't mind some C# developers either frowning or laughing at you.
