With the abysmally low margins typically made off of keyboards and mice along with the fact that the highend of the market is driven by desktop gamers, I think you're going to see plain USB Keyboards and Mice sticking around for a long, long, long, long time. Hell, I can still buy some of my favorite keyboards with a PS/2 connection or with an included adapter.

I've been using external devices for these with my macbook for years.

Edit: In fact, I think this applies to almost any low-cost, low-margin pluggable. Laptop coolers/fans are another. Either USB-C is going to kill the market for these or you're wrong.