I'm sympathetic, but I think the approachability problem says more about programming culture than it does about parens. People optimize for the ease-of-use case (read: syntax) over factors which have much more fundamental implications throughout the lifetime of a piece of software.
I mean, learning syntax is really not where we spend most of our time while writing software, right? All else being equal, the amount of time it takes to learn new syntax is orders of magnitudes less than the time you spend, in aggregate, finding and fixing bugs. So it's a misguided trade-off, and (fortunately or unfortunately) I don't think swapping square brackets for parens (or whatever) is going to change people's preferences for what looks and feels easiest for them.
I mean, learning syntax is really not where we spend most of our time while writing software, right? All else being equal, the amount of time it takes to learn new syntax is orders of magnitudes less than the time you spend, in aggregate, finding and fixing bugs. So it's a misguided trade-off, and (fortunately or unfortunately) I don't think swapping square brackets for parens (or whatever) is going to change people's preferences for what looks and feels easiest for them.