I tried changing the pom.xml to use struts2-plugins 2.0.2-SNAPSHOT parent and depend on xwork 2.0-beta-3, which are the latest versions to date, however it fails to compile.
org.apache.struts2.webflow.WebworkFlowAdapter class seems to be calling XWork's ActionProxy.getConfiguration() method, which was removed from XWork 2.0 beta.
Configuration config = invocation.getProxy().getConfiguration();
I'm quite new to XWork and SWF, so I might leave this for someone else to fix (if it's a bug).
Can't wait to use Struts 2 with Spring Webflow!