[capableweb]

I don't know, it makes sense to use different data structures for different purposes. (), [], {} are all different data structures (lists, vectors and maps) that are useful in different situations, so makes sense to have shorthands for them.

[dreamcompiler]

Maybe. What bothers me about this idea is that it doesn't scale: As soon as you need a fourth bracket type you're hosed, because there are no more on the keyboard.

With Common Lisp, you can define [ and { if you want to, but it's more common to use a reader macro character in front of an opening paren or a function name after it if you want different data structures. Those approaches scale.