OP specifically said the constraining mechanism was unique, hence why GP (and myself) are curious about what makes it more interesting/powerful than what exists in other languages like C#.
I do wish people would resist the reflex to overtly digress onto their own favorite programming language in any given programming HN thread. I'm not talking about insightfully comparing two languages; I'm talking about going completely off-topic because you want to talk about your own favorite language.
If this is in reference to my bringing up of C# - I did so in order to talk about whether or not Go has generic constraints which are unique (which would be awesome!). I used C# as an example of a language that has constraints that are the same as/as powerful as those in this Go proposal so as not to be making an unsubstantiated claim.