SML is great, but based on the UW paradigms course, I'd say it gets a lot of backlash from students wanting something common in industry.
Transitioning first classes from C to go would make great sense, but it looks like a lot of schools already replaced C with Java and C++ as first languages.
Personally, I do think there is merit in teaching a primarily imperative language first, if only to appreciate other paradigms later and get an inkling of what is really going on beneath your code.
What I took from the Coursera version of the UW course was that SML gets out of the way and let Grossman cover the material at a higher level of abstraction than language syntax. On the other hand, his Programming Languages class is not intended to be introductory.
I also thought SML worked quite well at that level, but I think the initial negativity on the forums about an unknown language reflected what to expect from a larger portion of 101 students.
I was in the second iteration. There were still plenty of people calling for a pony and M&M's for breakfast. I can only imagine the first iteration.
SML worked well because it's more or less dead. All the documentation is basically on a single unsexy website. There aren't a bunch of blogs cluttering up Google results or even much on StackOverflow. Racket also has a single Canonical source and good clear documentation and not much noise.
I can't say the same about the Ruby ecosystem, where I saw this crazy construct in lieu of a call to super posted in a forum question. The TA asked how the person arrived at it. I knew the answer because I had landed at the same StackOverflow page from Google earlier in the week. Which is not to knock Ruby. I understand why people describe it as beautiful.
Transitioning first classes from C to go would make great sense, but it looks like a lot of schools already replaced C with Java and C++ as first languages.
Personally, I do think there is merit in teaching a primarily imperative language first, if only to appreciate other paradigms later and get an inkling of what is really going on beneath your code.