The point of Base64 is to represent binary data using a familiar character repertoire. At least for the latin-script world, any collection of 256 characters won’t be a familiar character repertoire.

Who told you that? Don’t talk to that person anymore.

Base64 and uuencode before it are about transmitting binary data over systems that cannot handle binary. There are a bunch of systems in the early Internet that could only communicate 7 bits per byte, which is why uuencode uses only printable low ASCII characters. Has nothing to do with familiarity.

Systems that supported eight bits per byte were referred to as “8 bit clean”, to distinguish them from legacy systems you might still have to support.

PNG file format was specced in 1995, and it was still worried about 8 bit clean transmission. The first byte of the PNG magic number has the high bit set because they didn’t want the decoder to even have to bother with broken PNG files.

> Base64 is also widely used for sending e-mail attachments, because SMTP – in its original form – was designed to transport 7-bit ASCII characters only. Encoding an attachment as Base64 before sending, and then decoding when received, assures older SMTP servers will not interfere with the attachment.

I think it’s reasonable to assume that in a world with 9 bit bytes, someone may have chosen 8 bits for SMTP, or moved to 8 bit sooner. Which would give you at least Base128.