From the article, it doesn't seem like Go is trying to re-encode strings? Go is saying (correctly, IMO) that a UTF8String field in the Issuer is not the same as a PrintableString field in the Subject.

Ah, you're right, I was a bit confused by the bouncing back and forth between Go and OpenSSL and the title, "Fooling Go's X.509" when in fact on re-read Go appears to be doing the right thing and using a strict compare while OpenSSL uses the open-to-manipulation compare.