RFC7421 (which is Informational) calls out RFC 6164 (not 6141!) as an
exception.
To be precise it says:
The de facto length of almost all IPv6 interface identifiers is
therefore 64 bits. The only documented exception is in [RFC6164],
which standardizes 127-bit prefixes for point-to-point links between
routers, among other things, to avoid a loop condition known as the
ping-pong problem.
I would suggest adding a similar exception statement in 4291bis.
and then next year we will go through another draft and have another
exception. just get rid of classful addressing. we went through this
in the '90s.
randy