I fully agree with this. If a system cannot be extended by some external team using only external extension points, all claims of modularity and architecture ar

I fully agree with this. If a system cannot be extended by some external team using only external extension points, all claims of modularity and architecture are idle talk. I tend to use MEF (on .NET) and OSGi (on the JVM) not because I actually need extensibility, but because I want to enforce certain architectural constraints.