One simple improvement we could make without requiring major changes would be to show the inheritance in the autocomplete dropdown, a bit like the following:
We would have to consider several factors carefully, such as: should the autocomplete match on any term in the inheritance chain, or just the last term? How should we handle narrow view widths, such as on mobile devices? Do we wrap the full term to the next line, or add ellipses (either to the earlier/parent terms, or to part of the middle) to part of the inherited term? And so on.
Still, this would allow for more context without significant redesign. Since SKOS does not really support subdivisions (unless you hardcode them as a single term), adding support for subdivisions would mean needing to find and replace the export formats available as well, which starts to look like a much bigger job.
One thing I do like about the ArchivesSpace interface is that you have an option to open a modal and browse all terms while in the description edit page, and even add terms from the browse modal:
Modals can sometimes lead to a frustrating user experience, and can be difficult to maintain (depending on how they are implemented), but a super simple and affordable option for AtoM would be to add a button above the edit fields that says "View terms," that simply opens the related taxonomy browse page in another tab. Users would not be able to add terms directly from there, but it would at least offer users the option of quickly getting to browse the terms without having to leave the edit page of the current record.
The idea behind both of the above suggestions is primarily to find ways to enhance the usability without requiring major redesigns, thereby keeping the costs more accessible. There is certainly much more that could be done, but the more complex we get, the more those changes cascade throughout the application and require greater resources to implement.
I would also love to hear other perspectives from our community - how could we improve term management in AtoM? What would be your priority enhancements or fixes?