Once generics get introduced into the language, you can write a generic map function which can take a []T and a func(T) U to return a []U. While it's not as elegant as a list comprehension, it's nicer than writing a for loop every time. Although, I can't remember what the performance impact of closures are in go, so this might not be a cheap operation.
In practice, no one will do this, unless there happens to be a function with the correct signature already available. The lambda syntax is so verbose that it's easier to just write the for loop.
Another problem is that tons of Go functions return (value, error), and it's not clear how such functions should interact with a "map" function. Return all the errors in a separate slice? Stop at the first error? What if you only want to stop when the error is io.EOF? etc.