I think that requiring line breaks is silly. Most Base64 parsers
handle arbitrary whitespace. OpenSSL's parser is just plain nasty
(yes, I once made the mistake of reading the code), but even with
OpenSSL's parser there's a straightforward (if ridiculous) workaround:
http://subvert-rpki.hactrn.net/trunk/rp/rcynic/bio_f_linebreak.c
http://subvert-rpki.hactrn.net/trunk/rp/rcynic/bio_f_linebreak.h
I really don't think we need to enshrine OpenSSL's warts in the
specification.
I prefer Richard's option 2 (allow but do not require linebreaks),
which is what RFC 6490 RP implementations had to support anyway.