They won't see people switching to Swift uniformly. There are trillions of lines of code written in Objective-C, and programmers already know it and are comfortable with it. There are no tools for migrating code from Objective-C to Swift, much less the hodgepodge of mixed C, Objective-C, and sometimes C++ that quite frequently occurs in real-world apps, so for the foreseeable future, you'd end up just adding Swift to your existing apps, which means you now have three or four languages mixed in one app instead of two or three, and now one of them looks completely different than the others. I just don't see very many developers seriously considering adopting Swift without a robust translator tool in place.
I do, however, expect to see Swift become the language of choice for new programmers who are coming from scripting languages like Python and Ruby, because it is more like what they're used to. In the long term, they'll outnumber the Objective-C developers, but the big, expensive apps will still mostly be written in Objective-C, simply because most of them will be new versions of apps that already exist.
BTW, Apple never really treated Java like a first-class citizen; it was always a half-hearted bolt-on language. My gut says that they added Java support under the belief that more developers knew Java than Objective-C, so it would attract developers to the platform faster. In practice, however, almost nobody ever really adopted it, so it withered on the vine. Since then, they have shipped and subsequently dropped bridges for both Ruby and Python.
Any implication that Swift will supplant Objective-C like Objective-C supplanted Java requires revisionist history. Objective-C supplanted C, not Java. Java was never even in the running. And Objective-C still hasn't supplanted C. You'll still find tons of application code for OS X written in C even after nearly a decade and a half of Apple encouraging developers to move away from C and towards Objective-C. (Mind you, most of the UI code is in Objective-C at this point.) And that's when moving to a language that's close enough to C that you don't have to retrain all your programmers.
Compared with the C to Objective-C transition, any transition from Objective-C to Swift is likely to occur at a speed that can only be described as glacial. IMO, unless Apple miraculously makes the translation process nearly painless, they'll be lucky to be able to get rid of Objective C significantly before the dawn of the next century. I just don't see it happening, for precisely the same reason that nine years after Rails, there are still a couple orders of magnitude more websites built with PHP. If a language doesn't cause insane amounts of pain (e.g. Perl), people are reluctant to leave it and rewrite everything in another language just to obtain a marginal improvement in programmer comfort.