This should depend on Bug 36525 as notices and slips has become much more than just notice/slips. If there is not message_transport_type for things like `OVERDUE_FINE_DESC` we should not display 3 accordion tabs for Email, Print, and SMS. In these instances it would be nice to just have 1 place to add your customization. It would be much less confusing. Also many 'slips', like ISSUESLIP, don't need the 3 different areas to add content either.
+1, it makes sense to generalize this one tool that already solved many of the problems of inserting variables and having template toolkit support. (security implications and editor assistance). The alternative is arbitrarily having some parts of the Koha not having access to that despite having similar needs. Or duplicating elsewhere what this tool does.