I do see what you mean, and don't totally disagree, but to extend your "smartphone" metaphor I see your hypothetical as akin to someone looking at a like an old

I do see what you mean, and don't totally disagree, but to extend your "smartphone" metaphor I see your hypothetical as akin to someone looking at a like an old school Motorola Razr and saying "in the future these will be ubiquitous". Not necessarily wrong, but not exactly right either. The implementation of personalized assistants could take lots of different flavors, and the ultimate usage pattern which is settled (to me) seems likely to be outside any of our current models.