The syntaxes were pretty much unused in KF5 and because the usage help for KRunner is in progress(https://phabricator.kde.org/T13073) we stumbled upon some issues.

Using the syntaxes for the single runner mode is hacky: We have multiple syntaxes in the runner and one default one. From this default one we grab the first example query and use it as a template in the UI. (See RunnerManager line 866) . But in the current implementation of the frontends we don't even allow empty queries.

So maybe we should just use the syntaxes for the usage help only, deprecate the unused methods and consequently remove this functionality in the RunnerManager in KF6.