I'd like to see the web take back some mind share from native apps. We have a huge split of effort between web apps and installed/native apps; and no really good reason for that to be happening. From a technical perspective, browsers are getting a bunch of great APIs giving access to hardware and OS features. This could always have been the way, instead of having years of walled gardens driven by intentionally-created limitations on web browsers. Some will argue that walled gardens allowed developers to get paid; but in reality just a small number get most of the money.
From a business perspective, the web is still struggling to find a decent business model for publishing content. The only thing that has truly worked for long periods is "whack ads on it". There are individual cases where some other approach has worked at least for a while; but by and large it's ads or more ads.
So there needs to be a business breakthrough. Some way for content publishers to get paid fairly for what they do, that's more nuanced than increasingly-aggressive or increasingly-creepy advertising strategies.
I know I was meant to say VR! 3D! Yeah! ...but that's not going to take off until they can make properly-affordable, lightweight hardware and an experience that doesn't make a lot of people throw up. That's a pretty big deal breaker, really.
Edit: also I'd like the web to finally embrace accessibility.