Interesting topic! Personally I only agree with half of it. It would be indeed great if at least some add-ons became part of NVDA, and I would include Screen Curtain among those.
On the other hand, I totally oppose the exclusion of the ducking function. It’s extremely useful, especially with services like Youtube or Google Play Music. Often it’s the only way to hear the screen reader without having to close everything else.
Let’s see what other opinions come up!