That's normal. Chiasmus was developed by the BSI (more or less
equivalent of the NSA) and so all their work is classified by default.
They only declassified a Window$ binary. There's evidence towards the
existence of a GNU/Linux command-line version, but said version appears to
be still classified and thus not publicly available. And the source code
appears to be classified entirely. So I don't think Chiasmus will be
available in Fedora any time soon.
PS: And the only reason it's supported at all in KMail is that the companies
working on KMail encryption were contracted by the German BSI and the BSI
apparently requested that option to be present for their internal use.
If the presence of the useless option really annoys or confuses users, we
could of course patch it out, but I don't think it's worth doing that.