RFC 5952: A Recommendation for IPv6 Address Text Representation
says "The characters "a", "b", "c", "d", "e", and "f" in an IPv6 address MUST be represented in lowercase "[1]
One Reason for this, is that it can avoid redundancy if you submit a hexdecimal nummber by phone.
"However, when a letter is spelled uppercase,people tend to specify that it is uppercase, which is unnecessary information."[2]
If you care about typography and think mixing lower-case letters with upper-case numbers, you could argue, that oldstyle numbners aka. lower-case numbers could be a better fit.
Since the RFC came 42 years after the magazine article, and 27 years after I sold my first computer program (with data in hex), I'll just consider myself old fashioned.
says "The characters "a", "b", "c", "d", "e", and "f" in an IPv6 address MUST be represented in lowercase "[1]
One Reason for this, is that it can avoid redundancy if you submit a hexdecimal nummber by phone.
"However, when a letter is spelled uppercase,people tend to specify that it is uppercase, which is unnecessary information."[2]
If you care about typography and think mixing lower-case letters with upper-case numbers, you could argue, that oldstyle numbners aka. lower-case numbers could be a better fit.
[1]https://tools.ietf.org/html/rfc5952#section-4.3
[2]https://tools.ietf.org/html/rfc5952#section-3.3.3