Shouldn’t data_readers be automatically required? Currently I have to ensure elsewhere that data reader function’s namespace is loaded before using the data reader, otherwise it complains about “Attempting to call unbound fn”

Yeah, you have to load the ns. I wasn’t around when that stuff went in, but need to consider the security considerations of auto loading

is there an issue for that, or should I write about data readers on http://ask.clojure.org?

I'm not aware of an issue