OSGi is now part of AS7 master. The OSGi subsystem starts ON_DEMAND by default and comes up when the deployment layer detects a valid OSGi bundle deployment. From the user perspective this happens when you drop a bundle in the 'deployments' folder.
The subsystem can also be configured to start eagerly like this
<subsystem xmlns="urn:jboss:domain:osgi:1.0" activation="eager">
...
</subsystem>
Having said above, there was however a small piece missing in the merge to master. This patch fixes it
http://github.com/jbosgi/jboss-as/commit/7ea8d19d507360976790dfc78dd93e8ecd182cb3
As always, the latest stabe OSGi integration is available at: http://github.com/jbosgi/jboss-as/tree/jbosgi
cheers
-thomas