Another problem is that currently it is propagated, but daikichi is
not a dependency of fortunes-jkirchartz.

Well, it is a dependency in that you need a fortune program to read the
quotes.  Should I instead add a meta-package that propagates both?

I think it's a situation like 'man-pages' and 'man-db'.  'man-pages' has lots of man pages and 'man-db' has a reader for man pages, but this does not make man-db a dependency of man-pages. (Similarly, IceCat is not a dependency of the web page https://guix.gnu.org). OTOH, daikichi is the only reader for the fortunes so the situation becomes a bit incomparable.

I suppose there's some convenience in propagating daikichi, but currently AFAICT the policy for those situations appears to be to not propagate it (and neither create a meta package reader+information), so unless there's some agreement on guix-devel@gnu.org to change that policy to go for meta packages or propagation, I don't think the individual fortunes-jkirchartz package should do that.