Thanks for the feedback! I definitely agree. I've added support for the symbols you suggested (and a couple more, like & for passing inout arguments).

How I implemented this was writing YAML files that get compiled. Each entry has a name, an array of strings for tags, and the code sample itself. When you type a query, it shows prefix tag matches first, followed by non-prefix tag matches. So now when you type '?', you should see optionals, ternary, nil coalescing, etc.. but when you type '??', you're left with only nil coalescing.