I agree it's probably best not to require Spring 4 in a point release. For Camel 3.0, it might be doable. In the meantime, I don't think it's a good idea to prevent folks from using Spring 4. I think the easiest way forward is to create two modules: camel-test-spring and camel-test-spring3. The former compiles against Spring 4 and the latter against Spring 3. You could switch it so camel-test-spring defaults to Spring 3, but camel-test-spring4 doesn't seem to be forward-looking, as you hopefully won't need a camel-test-spring5.
I've made this change in a fork and it works in my project. I can upgrade to Camel 2.14-SNAPSHOT and CXF 3.0 with Spring 3.2.8 (by using camel-test-spring3). I can also upgrade to Spring 4 if I use the upgraded camel-test-spring.
Here's a pull request that has this change: https://github.com/apache/camel/pull/199