I'd like to have the ability to use a custom field in multiple apps, or even potentially multiple solutions. I contacted support and they said that is under review on the internal roadmap, and I should maybe create a feature request to gauge interest.
Support said the current idea is to create predefined lists you can import as field templates. I like that idea. It would be great if the lists can be defined and accessible at the workspace level so they could potentially be used in any solution. Also, maybe have a settings option with a UI to see all predefined lists for each field.