But the nice thing about UTF-8 is that this proposal isn't really a "complication", but a minimal and natural extension of the original idea to allow more than one lead byte.
Allowing more than one lead byte is a complication of the existing standard. As many others have pointed out, we have plenty of coding space without that (e.g. by allowing 5- and 6-byte UTF-8 again), so the case for the extra complexity is currently not compelling.