So he seems to not like Go or Arc. I like Go a lot but I am always interested to hear other opinions. While I'm sure he has good reasons for this, I wish he would have included them. It seems like he's saying "I don't really like this, here's a link!"
Go is not in the mind stretching camp, it's just practical. It's made from existing ideas that you would have seen in other languages that came and went. So in that sense it's not interesting and yet it is.
Go is mind-stretching in its practicality and pragmatism.
Most (but not all) its ideas have been implemented before elsewhere (but then, that is almost bound to be true of any new language).
But the real 'innovation' is in the careful selection of those ideas and in how well they work together _in practice_.
This puts off people who are used to this or that feature in other languages, Go is not about checklists of features or abstract arguments about how languages should be, it is about what works really well when you sit down to write (or read) code.