There's been plenty of discussion this week about this proposal to make Swift classes final by default. Michael Tsai has a comprehensive collection of all of the commentary here, as usual. Go and read it!
My gut reaction to this was that it was a terrible idea, but the more I read and think about it I'm not sure it's as big an issue as it might first appear to be. I also trust the Swift team to make the right decision for the future of the platform, even if it doesn't feel quite right immediately.
Anyway, the proposal is back in review at the moment, so the decision isn't yet... final. 😆 (Sorry... I couldn't resist!)