Well, I guess that’s where we disagree. IMO it’s a 50/50 if it will ever replace USB-A. I think it will just replace microUSB and leave the full-size port alone, but since some manufacturers are pushing it so hard, it will probably also see its place in laptops, and then slowly start moving towards other form factors. But that won’t come fast. That will be painfully slow because of the variety of different USB devices we have now and how much it would need to replace.
My prediction: this year it becomes mainstream in phones, maybe in 2019 things like mice/keyboards will start being made for it, and IF it ever happens, it would only replace USB-A in 2025 or later.
To clarify, we will probably have some “hybrid” peripherals soon, like USB drives with USB-A on one end and C on the other. But they will, of course, be more expensive than regular ones, and few people will actually have them. Think of it this way: you go to a shop looking for a flash drive - you see two options: a cheaper one that works with all your computers (USB-A) and a more expensive option that also works with your phone. I’d pick the cheaper one any day, because how often do you need a flash drive for your phone?