if only all of those things were fully flushed out in the various browsers... for instance, it disheartening to realize that it's been 15 years already and useful form elements like date(-time), phone, and email still don't have reliable and complete cross-browser behaviors, validation (i know it's hard, but still), and styling/event hooks.
True, support still isn't perfect. The calendar/date picker stuff is especially annoying here, since it really should be easier to customise and more similar cross browser than it currently is.
But most of the things mentioned do work in more browsers than not, and you can use them without worrying the site will break in almost all cases. The new semantic elements will never have issues (unless you're trying to target IE8 or below), the validation works fine in pretty much all modern browsers (as do simple styles for it) and support for the picture element and srcset are pretty good too.
The likelihood of anyone using the Blackberry browser or IE mobile is small enough to ignore.
