Honestly, the title is terribly clickbaity and OP should feel bad. Especially because it looks like a well estabilished library with 3.8k stars that doesn't need it.
But that makes me wonder: is Socket.IO so slow that can actually hurt performance in a "normal" use case? And when does it hurt?
I see that the title is to catch the readers rather than actually to state the end of native apps, if you admit that they "still have a few capabilities that mobile apps will not have for a potentially long time".
It's not that device manufacturers have never tried the "all-web-tech" road in the past - it's an effort as old as WebOS - but there are apps which are *explicitely* thought for devices, and aren't suit to live on the web in any form. Like a file explorer, for example.
Honestly I have no idea native apps are doomed, or even will be relegated in a small niche. In my opinion, it's way too soon to tell. We still don't know if PWAs will ever catch on, among developers *and* users. Safari doesn't even support service workers at the moment.
One thing, for sure, is that we should try to develop PWAs because they *do* look cool!
In short, it makes background images centered, non-repeating and covering.
If the browser supports CSS3, that doesn't need a jQuery plugin: all you'd need is a CSS class!
The only "useful" part is the fix for IE8- for background-size... which works as expected only if it's set to `cover`. If you want something else (because it's an option you can override), you're out of luck.
Definitely a badly designed plugin.