Google and Microsoft do this too when you enable real-time searching via the address bar, but both are pretty good at letting you know it happens. Doesn't Safari have some kind of first-run experience where the user gets some notice on this?
You can bet they are going to build it though and it'll look nice.
With the right expertise on the team and some decent exposure to real users prior to the wide release, they may be able to deliver something that people enjoy using. The micro-features that delight users are something that Apple has traditionally done well, and are also the type of thing that go a long way in a product like a search engine.