Julia functions are often so generic and polymorphic that it’s hard to determine function input-output without running type inference (and sometimes not even that is enough). You can get an enormous amount of hits, because people often write code that is completely generic, with only an inkling of an idea about what input/output it will take and produce.
When I replied to your question I didn’t just rely on memory and experience, I used the perspective shift I recommended. Don’t ask about types, ask about functionality. You want to convert? Search for convert! That’s pretty straightforward.
I don’t oppose your suggestion, but I’m not sure if it will be quite as useful as in Haskell, where it seems like input/output types of functions are more common and available.