I'm maintaining two Add-Ons with around 20k active users. I agree with his predictions, but I also find it hard to give to much attention to voices like the one expressed here.

It's hard for me to tell how much of this is genuine concern, or just how many donations or how much income he will loose because of this. I never see numbers from these Add-Ons. The one in question here has 1,300,000 daily active users.

Sure, if I make $1500 per month on an Add-On, I would be very upset if things change. Then I'd rather see the XUL/XPCOM stuff around for another 15 years.