I was not very involved in this. I still prefer s-expressions.
Anyway, my main initial concern was how to make good macros without s-expressions. There is a nice video by Matthew Flatt in RacketCon 2023. The first 6 minutes and 20 seconds are internal stuff, so skip to the 380s that I added in this link: https://www.youtube.com/watch?v=OLgEL4esYU0&t=380s He takes like another 6 minutes to explain the general idea and make some wishes, and then at the 12m mark he defines macros in Rhombus and makes the wish real in just 2m (with some enhancements later).
I mean, M-expression was proposed right from the start.
Then there is nothing special about having the brackets around. To start with, text can be just as readable:
And one can use stack base syntax, or define a static default arity to infix notation, example two, so `times plus 1 2 3` is not ambiguous and is really clearly like (1+2)*3 with such a convention. Then you can shift arity with reserved word so `unary plus 1` is like `+1` or `arity 5 action one two three four`, or going back to explicit marker like `(` and `)` or `do` and `go` to group stuffs without explicitly quantified numbering.