I see it as a wealth level thing. People will still be buying $30 Canon printers at Walmart with USB-B ports and USB-A flash drives in 20 years. Not everyone buys their entire family the newest, most expensive hardware every 2 years. It'll be ages before USB-C and USB 3 hardware becomes as cheap as the massively produced USB-A/B and USB 2 hardware.
A printer with a USB-B port can be plugged into a USB-C port. Only the cable needs to change, not the printer. After buying my Macbook with 4 USB-C ports I simply replaced the cables for the various devices, and I almost never need to use any adapter/dongle at all.
