Siri had such huge potential, but even Apple doesn't take it seriously. When I saw it demoed I was so impressed. I do use it for reminders and some other tasks while I'm driving, but it doesn't offer anything the competition can't at this point.
And? Apple might not be trying to make something super special at this point. After all, who cares is it has AI that can make it seem like your best friend if the key systems are borked. Baby steps are sometimes best.
As for this position, if true it sounds more like an add on to the many engineers they have in the mix. Someone more of a creative type to think up natural language input folks might use and give back more natural replies. They know that folks like to prank Siri so why not include some appropriate replies. Better to have one person working on this than the key engineers who should be working in her reply times, search results etc.
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[Edit: I feel I need to qualify this response. My problem is that it feels like it's been a while since Apple wowed us with a bit of true innovation.
And how are they supposed to do that. Short of building the T-100, where is this innovation supposed to come from. Everything they would be doing would just be tweaking an existing thing.
Heck even building the t-100 would be true innovation since they didn't think it up but copied the idea from a movie (same with UI glasses, watches, TV walls etc. all from books, movies or TV shows)