Similarly, when there are no extension points, extension get hacked in (= "if" everywhere !)
Here is my experience with architected extension points:
1. Generally the first extension point used set the trend, other developers will follow the "pattern" blindly. Hacking to make it fit rather than use another more appropriate extension. That is both bad and common (everyone has had to work with too little time)
2. There is often a sharp refocus close before or after release 1.0. A lot of the extensions disappear at that stage (demo, experimental feature, cross-platform/framework support, performance targets are set, security infrastructure is decided, server setup, integration test env. available instead of simulated, ...). Structural change (like removing extension point) become very difficult to justify after release 1.0.
3. Technical debt is very often called "selling feature" at management level.
