golang likes to reinvent the wheel and call it something else. We've already seen it with exceptions (which they called "panics"). Contracts already mean something else (see contracts in C++, C#, D, etc.).
What they're proposing here are basically trait bounded generics. They just don't want to use the word "generics" because of the following attitude:
"The key point here is our programmers are Googlers, they’re not researchers. They’re typically, fairly young, fresh out of school, probably learned Java, maybe learned C or C++, probably learned Python. They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt."
What they're proposing here are basically trait bounded generics. They just don't want to use the word "generics" because of the following attitude:
"The key point here is our programmers are Googlers, they’re not researchers. They’re typically, fairly young, fresh out of school, probably learned Java, maybe learned C or C++, probably learned Python. They’re not capable of understanding a brilliant language but we want to use them to build good software. So, the language that we give them has to be easy for them to understand and easy to adopt."