From a partner:

"We've added our journal holdings data to multiple 590/a fields. We'd like these
to display in both the search results pages and in the individual bib record in
the OPAC and the staff client. The information is displaying in the title
detail tab but we don't want to have to click to it; we're used to seeing it
immediately with the title information. Attache jpg shows Title Details tab
with 590/a information, search results example with note where to display 590/a
and bib record with note where to display 590/a"

Two suggested ways to tackle this:

If XSLT:

The best way to display the 590a in a community-friendly way is to allow
user-uploaded XSLT.  This is comparatively simple, as we'd just need to code up
the file upload scripting, and then point the XML parser at that XSLT instead
of the built in one.  It would involved writing XSLT, which is unpleasant, but
we would help with that, and a page could be added to the Koha wiki to share
completed XSLTs

If Normal view:

For this method, I'd go with teching up the Keyword to MARC mappings tool and
add more supported Keywords.  This would again not be 590a-specific, but rather
a matter of placing the keyword tokens into the code in the right places, then
configuring those keywords to map to the right MARC.  "Keyword" is probably not
the right term to be using here, so renaming might make things clearer for the
continued use of this functionality.