It is likely more that the Safari team anticipates non-scrupulous companies taking advantage of an option to add a default search engine inline. Things like mod

It is likely more that the Safari team anticipates non-scrupulous companies taking advantage of an option to add a default search engine inline. Things like modal prompting and site-specified explanatory text are exploited these days. Likely the best bet would be a web extension manifest value to expose a potential search engine. That would mean on iOS that you still need to publish an app for your search engine option to show up.