Clojure for GAE is nice. Its really cool that you can use this library with all ring-bases webframeworks (witch are basiclly all clojure webframeworks).
I don't now how python is for the appengine but clojure is much more better then java. The leiningen plugin that this library provieds is great.
Have you actually tried using clojure? Last I heard, relying on a large jar like clojure meant you spent 29 of your request's 30 seconds loading the jar and had only 1 second to do real work before GAE killed you.
I'm looking at a live App Engine console for the Clojure app I'm working on right now, and I see cold-start JVM times varying from 3 to 10 seconds. Although this is a lot, with the latest App Engine, you can (1) pay $9/month to have 3 JVMs always running, and (2) your app receives warm-start requests which will cause a new JVM to start before it's needed.
In other words, your users should (almost?) never pay the penalty for a JVM cold-start. A single JVM stays around to serve requests as long as App Engine detects sufficient load to justify the resource usage.
The Deadline (https://the-deadline.appspot.com) is written in Clojure and runs on GAE. If this problem still persists, somehow they must have found a way to deal with it.
I gave up on Clojure running on App Engine a year ago because I could not get the loading request time below 3 seconds. It is not as bad what you describe, but it was a problem. The loading requests happened frequently enough that users noticed the lags.
I don't now how python is for the appengine but clojure is much more better then java. The leiningen plugin that this library provieds is great.