Rejecting the typeclass pattern won't kill off the Scala 2.9 cross-builds, but if everything must use `Future` then it will effectively kill off the synchronous client implementations (we currently support Apache HTTP and plain old java.net). That may not be a big deal, although I recently used the java.net client on an App Engine application because I know that on GAE, using java.net actually delegates to Google's UrlFetch service.