One downside compared to micro-usb in my experience was having my macbook stop charging after (apparently) using the wrong usb-C adapter. I don't think I ever worried about which actual adapter I used for a micro-usb device, but I guess you have to be more careful which usb-c chargers you use... another example: http://arstechnica.com/gadgets/2016/02/google-engineer-finds... )
I don't think as a connector it has the polish of the lightning adapter, but I also don't think it would be a disaster if Apple switched to using it.