Bug 41539 adds item barcode content to the "Holds waiting" message on #circ_circulation and #pat_moremember. It occurs to me that it would be nice if the content of this message could be controlled using a template through the HTML customizations tool or through the notice and slips templates. That would allow libraries to decide what content to have in that message without a developer having to write a patch for Koha every time someone wants to add or remove content in that message. It seems that this idea could be also applied to other messages in Koha. It would be nice to give more control over the content of messages and modals to individual libraries rather than forcing all Koha users into a one-size-fits all system.
Like bug 39860, bug 40659, and bug 19838, this should use a scrubber profile to protect against XSS vulnerabilities.