I certainly agree that deprecating millions of lines isn't a great way to win over developers. Apple hasn't deprecated Objective-C yet though, and I think both Swift and Objective-C will be supported side by side for a long time yet.

Apple is usually quick to deprecate (which does have its own advantages), but given that a large part of their own tech stack is built on Objective-C, I think they'll play the long game here. I would be surprised to see it deprecated before the end of next decade (although I wouldn't put it past Apple either...).