It absolutely is.
If you don’t make extensibility a core philosophy every step of the way, it disappears very quickly.
Bethesda would need to completely rework their tooling and engine to block out this core philosophy.
They are reworking their tooling and engine constantly.
If they weren’t making a deliberate point of making extensibility a priority, it would disappear on its own as development that didn’t make it a focus left it behind. It doesn’t just magically happen. It’s because of good process.
We shall see with CreationEngine 2 if they would removed that facette. But I doubt it since its the essential core of that engine to be extensible.