Readers should keep in mind that cython originated from the sage codebase. I bet there's lots of gems in there that many people would like to play with independently of sage.
Will you need to release these modules under the GPL?
Recently we did factor out the code in sage for Cython signal handling (so you can hit control+c to interrupt blocking Cython code!) into a separate library called cysignals. We changed the license from GPL to BSD when doing this!
