Did auto-complete in search solve this? You can start typing the category name/slug and hit tab for it to fill out to the correct syntax…
However, I bet the quotes are throwing off auto-complete, I tested it on my sandbox and typing “#site feedback” followed by tab changes it to site feedback
Whether it is a bug or a feature is up to you to decide. To me it is a broken implementation, but if you consider it to be a feature request, that’s fine too.
That does not appear to work with “category:”. I can type “#que” to complete to #questions, but I cannot type “category:que” to complete to category:questions.