Related to the "Cutting the Mustard" of BBC part in the talk where they serve a core set of html/css and then depending on browser capabilities load additional

Related to the "Cutting the Mustard" of BBC part in the talk where they serve a core set of html/css and then depending on browser capabilities load additional js/css. What are people recommending for progressive enhancement these days? For sites that don't need a whole lot of js, but enough that just slapping on a bunch of jquery lines would get too messy. E.g. when you want to support sorting tables or saving forms without reloading the whole page. In other works, using js merely to make the experience smoother. Besides the points mentioned in the talk, setting up and maintaining a build pipeline for a fronted framework and maybe even server side rendering with it is just a vast overkill and unnecessary increase of complexity for the given problem. I used to use backbone.js for those kind of sites, because its view layer worked pretty well on already existing html and letting you fallback to it, while giving you more structure and modularity than plain js/jquery.