The only one not mentioned I think should be utilized more is properly names in html forms. Everyone has gotten used to just doing things in javascript when a lot of times if you name the fields in a correct way, you can do a simple form post and let the backend validate it with little to no modifications (hopefully none if you did it correctly).

I think the big issue with some of items listed is not all the browsers either implement it or they implement it differently. I'm sure your first instinct will be Safari but Chrome, while it may implement a lot, tends to do it quite different than the others. The date picker in browsers is one feature that comes to mind.