Adding commentary with additional context in hopes this thread surfaces in future search results by other users; and will copy it on the other submission.
I think "typehead" is a misnomer for what is needed; because what's needed would be a different functionality than the existing typeahead object (limited to one value only).
We want the ability to tag keywords or metadata to a wide assortment of object types, including projects, documents, issues, notes, users, and more. This can currently be done as a hack in some object types using a hashtag and text string combo that can be searched against, but it requires the user to remember what those codes are, different object types get the keywords applied to different parameters, and it's a very "hacky" solution. Would love to have this experience formalized and made consistent across multiple object types.