Study fails to consider one thing... Flash
A lot of the technologies that are being cited as "useless" in the study as part of efforts to be able to deliver a plugin-free experience - that is, to end reliance on things like Flash.
Along the way, this turned into a bloated mess, but some of these lesser-used technologies are essential if we want to truly be rid of the need for browser plugins.
Some of them aren't more widely used because they are definitely very niche. -but they are starting to see use - WebRTC is being used to bring videoconferencing like Skype into the browser, the various specs related to video are being used to deliver Flash-free video and are used on video streaming sites already, WebGL and the gamepad API are there to unseat Flash's stranglehold on gaming, and so on.
On the other hand, quite are few of these I recognize as being central to Mozilla's now-defunt FirefoxOS platform - bits and pieces that were implemented to make web pages behave like native apps which were rarely used and possibly not even widely enabled outside of FirefoxOS apps.
There's definitely room to trim some fat regardless. Of the features mentioned, a lot of them are excessively complicated, many of them are redundant, and many more of them need to be locked down under permission so that they don't get adopted widely by advertisers and malware. HTML5 video, for example, would be a better experience for users if it were behind a permission, so that videos never just start playing. There's only a handful of sites where I actually WANT videos to play on, places like YouTube.
Going forward what I'd like to see is the bare minimum of what's required to allow web applications to do things that currently require plugins, the simplest, smallest, cleanest,most easily audited implementation possible, and everything "niche" that an *average* website wouldn't use, locked down behind granular permissions, as Geolocation, Notifications,, Webcam/Microphone use, mouse capture, and other things already are.
I'd also like to see as much effort going into fixing the web advertising as has gone into these seldom-used features. Not killing it, fixing it, as that publishers get paid, users are not tortured, , privacy is respected, advertising ceases to be a malware vector, sites are not slowed to a crawl, and we no longer need an ad-blocker just to have a usable browser. I'd like to see a serious effort to impose a code of conduct and technical guidelines on advertisers, and war waged on those that don't fall into line. Something along the lines off this - audio/video ads only allowed to be delivered with audio/video content, otherwise static header and sidebar ad only, all ads to be surrounded by an advertisement border or watermark, etc. We've got to reach an end to the advertiser arms race, and, ans sites that break those and use abusive practices rules should start finding themselves in the malware blacklists.