Reason for replying to this post is because I had a similar 'wish' for a launcher in Budgie just a few months ago. If you were to ask why, I'd say it would be great for launching applications for one. Essentially this can be done through the Budgie menu by hitting the Super key; this opens the menu. (In lieu of a launcher). Start typing the first few letters of the application and a list of suggestions will appear with the first (most plausible) suggestion launch-able by hitting 'Enter', very similar to a launcher. Otherwise just arrow down to highlight application and 'Enter', again like you would in a launcher. For me this works relatively well and negates the reason for a baked-in launcher; the Budgie menu does this well.
In terms of searching for documents and/or files at the push of one button (or combination) however, that is something I do miss and for which I need a third party launcher, which I guess is what remains a silent wish of mine; to see this 'deeper search' functionality as part of Budgie and perhaps its menu.
This additional search functionality, or something similar, can be toggled on/off in the Budgie Desktop Settings?
Perhaps the team has no interest and if they do, will most likely sit at a very low priority. As much as I enjoy Budgie already, this is one those things that I believe would be great if it were part of Budgie.
Other than that, more than satisfied user here!