Note that both of those features use generics, which weren't present in the language before, so IMO Go just prefers to wait a bit before implementing useful features instead of having too many of them (ahem, Swift?)

I think that’s a bit of a stretch to say go will implement all the features of c# and Java because of a few new features. Go isn’t a frozen language, they just take a lot of time and discussion before committing to a major change.

The point isn't implementing all the features of c# and Java, rather doubling down on their simplicity mantra against all programming language complexity, only to revisit such decisions years later, because after all the other programming languages had good reasons to have such features in first place.

If you look back at the mailing list from earlier in the Go development you'll see that this was the plan. To start with as small and simple a set of features they felt was a necessary and evaluate more advanced features as the language evolved while trying to keep with the simplicity mantra when adding them. They wanted to evaluate the potential features in light of real work with Go.