Original title was 'treat colons as whitespace' which isn't a problem description but a (flawed) implementation approach
For JSON compatibility
known problems when no spaces - x:true and y:false
+1 from me.
Clojure is only hosted on the JVM; ClojureScript is hosted on JS VMs. If this is useful for CLJS, it should just be a CLJS feature.
-1 for this whole idea: that way madness lies....
If we keep adding syntactical oddities like this then the language will become unmaintainably complex. It's the exact opposite of simple to have lots of special cases and ambiguities that you have to remember.
If people want to use JSON that is fine, but then the best approach use a specific JSON parser/writer, not just paste it into Clojure source and expect it to work.
-1 for reasons mentioned by Allan Malloy and Mike Anderson
-1 Don't repeat the mistake made in Ruby...