I'm not necessarily requesting that 0x40 be fleshed out and clarified:
I'd be just as content to see it dropped. If, as I assume, the 0x40
is just the same as the 0x50 with a different (human) interpretation,
then perhaps we should just drop it. If people want to assign human
interpretations to their signatures, let them use notations.
As I remember, it stays there for the same reason that some other
signature types are there: for backwards compatibility with their never
being used. They are there for the same reason there is old stuff in my
garage -- we hope to use it someday.
I'm not sure spring cleaning is warranted, but it's easy enough, if
people think so.