Of course I'm not saying that people should stop working on what they want, they are free to spend their time however they want. I'm looking at it the other way: what if I want to create a protocol but can't be bothered to work on the UI, because I'm no designer ?

I'm not even talking about multi protocol clients because, as you said, it tends to level downwards rather than upwards. But if I could "fork" the UI and slap my protocol on it, instead of having to build it from scratch, I'd save a lot of time.