I would like project.search to allow me to specify slug as a constraint. Since I display the slug in the url of a 3rd party tool, I would like to similarly look up the project the slug refers to with this url. This used to be provided by project.query.
I would also like it if it would return the profileImagePHID either by default or as an attachment, which used to be returned by project.query. I display the project's custom image instead of its icon in my 3rd party tool, when it has been set, beside the project name.
I had been using project.query happily, but ran into the fact it returns an error when you query by icon. (A bug I don't expect will ever be fixed).
Because of the above problems, I can't transition all my code to project.search, and in the case of the icon bug, will be using project.search to get the project phids to then use project.query on as a workaround for now (ew).
That's also when I learned that your use of the word Frozen mapped to what I would have expected to read Deprecated. I realise the definition was on the API pages when you click through, I skimmed it because I expected it mean will not change (the opposite of unstable). Oh well, now I know.
I checked against https://secure.phabricator.com/conduit/method/project.search/ before submitting this, and searched for open tickets containing project.search