sometime in the future, Apple will begin releasing swift-only APIs. it's unclear that one should "drop everything", but swift usage will only increase in the future. in addition, as a company, it will become difficult to hire new people if you don't try to move to swift at some point.

ymmv, of course. i'm new to iOS land and i write objective-c exclusively during my day job. that being said, the difficulty in iOS development (in my experience) is not in the language, but the APIs, abstractions, and patterns - and they are the same regardless of whether you're using swift or objective-c