[1] https://www.amazon.com/AUKEY-Adapter-MacBook-Google-OnePlus/...
Here is what you can say about USB-A: * Ubiquitous; it is literally everywhere on this planet * Extremely cheap, reliable and easy to use * Not actually a competitor to USB-C/TB3 * Does not prevent the inclusion of USB-C/TB3 * Does not present packaging or legacy support issues
USB-C/TB3 is a great technology and I wouldn't want to buy a system without at least one port, but it is NOT a replacement for USB-A yet. USB-A will continue to be the most prevalent peripheral connector for long after these new MBP's are retired.
I will add: USB-C/TB3 is not exactly easy to use at this point. The convenience of using that same port for both protocols (TB3 and USB3.1) is introducing confusion. Not every USB-C port/peripheral is also a TB3 port/peripheral, this includes adapters and dongles. Additionally, the power options of USB-C/TB3 add another wrinkle: what hubs/docks/devices can provide enough power to charge specific devices? Not to mention that the current crop of USB-C/TB3 accessories don't always 'just work'[1]. Hopefully this will get better, but again it is not going to displace USB-A for a long, long time.
[1] http://www.apple.com/ca/shop/reviews/MJ1K2AM/A/usb-c-digital...