You should be able to reach any Go library, in fact. Aside from the Prelude, the Gsp Stdlib[0] is in fact just bindings to the Go stdlib that casts every value from interface{} into the required type. You can make bindings to any other library in this manner.
I do not know why Go-routines would not work, though I have not tried yet.
Another difference from the lisp you brought up (and the one I'm more familiar with, glisp[1]) is that Gsp is compiled as opposed to interpreted. This would ostensibly have speed features.
I am interested to test how this fares compared to these other Go Lisps and Clojure.