Although NetBeans' module system was on-par with OSGi, greater industrial support meant OSGi always looked like a better pick to outsiders.
Starting a while back I saw OSGi as the clear winner. Especially when Glassfish 3, an major Sun project picked OSGi instead of the NetBeans Module system, it was obvious OSGi was winning even inside Sun (although they were reluctant towards giving OSGi a too big stake in the upcoming Java 7 module system).
In the meantime NetBeans is getting native support to run OSGi bundles as well as getting ready to run inside an OSGi container.
Oracle wanted a common IDE extension API starting at least 2002 when they sumitted JSR 198.
Now, owning Java and NetBeans itself, they have it really easy to define the roadmap for both.
I estimate that NetBeans will be able to run inside an OSGi container by the end of 2010. We'll also see official NetBeans plugins distributed as OSGi bundles instead of NetBeans modules. In the end the NetBeans module system might become a deprecated subsystem.
Note: This is just my take at technology analysis. I have no inside information obtained via my NetBeans Dream Team membership or from Oracle.