possible. "printable" seems to be just the category but not that it was actually printed. of course some people print base64 of encrypted passwords (for offline storage) that would otherwise contain unprintable characters.
usenet exists since 1979/80 [1] and base64 was first described in 1987 [2].
MIME picked Base64 because uuencode uses a larger character set which, while fine for its original uu (Unix-to-Unix) purposes, made it less robust to cross-platform weirdness.
