These things were all known when development on Go began. But, as with so many other aspects of the language, if it wasn't known in the 80s/90s then it may as well not have existed.
I don’t know why people criticize Go for not being a cutting edge research language when that was very explicitly not the goal. Lots of things were available in the research at the time, and much of that has gone ~nowhere.
Starting with what they knew to work and iterating from there is wise.
