They should've just used Python 2's strings as UTF-8. No need to break every existing program, just deprecate and discourage the old Python Unicode type. The new Unicode type (Python 3's string) is a complicated mess, and anyone who thinks it is simple and clean isn't aware of what's going on under the hood.
Having your strings be a simple array of bytes, which might be UTF-8 or WTF-8, seems to be working out pretty well for Go.