I just don't think browsers are in a good position to implement advanced features like this, though. They are too general of a tool to be opinionated and if you aren't going to be opinionated I don't see how javascript isn't the answer.

What kind of autocomplete do you want? Which algorithm? What's the threshold if you're using some kind of "string distance" metric? What do you want to do style wise when you match portions of strings? What optimizations should be made for your specific case?

I don't see how a web browser is in a better position to make these types of features compared to a javascript library / web assembly.

It’s complicated but we did used to have people doing all sorts of nasty tricks with images to style checkboxes and stuff.

I think some attempts at incremental improvement would be nice, maybe as the drop down gained usage that would help decide it’s future direction. Right now it’s just kinda dead and hard to use unless you’re building developer UI or something.

All autocomplete implementations has different behaviour. It is not as basic as other fields such as text and checkbox. The same applies to date input which still often have custom implementations because the browser based input has ux issues or offers limited behaviour changes.