There's a huge spike of value created when you cross the threshold of "you really don't need to think about sysadmin stuff, you can just focus on the application layer."
Heroku was the first to cross it, and they do a bang-up job with Rails apps, but ever since it came out there has been this sort of question hanging in the air of "how does this generalize?"
A VM on something like Amazon EC2 was the best we could do at that time. It certainly generalizes, but you have to do quite a lot of sysadmin work to keep an app running healthily. Docker was an improvement on that, taking away some underlying system work. But then losing the security benefits of VMs and still, in the end, requiring a bunch of systemsy stuff.
Of course Heroku kept firing with its buildpacks supporting lots of platforms and a host of infrastructure provided as a service. But that doesn't really provide all of the control application developers need. You're sort of at the mercy of what infrastructure there's a market for, at market prices.
So what's happening is both sides are sort of pressing in to the middle... On the docker side trying to build general-purpose containers that can run on a shared foundation of rock solid system images, and on the IaaS side trying to do as much as possible over a network connection.
We will eventually meet in the middle, with a set of secure, well-defined interfaces between an application and the infrastructure it relies on, which is robust enough to handle the vast majority of software.
Then again, if you squint your eyes that's kind of what we already have. We're just slowly decreasing the surface area of those interfaces and increasing their security. What you're feeling is the pain of that surface area being still pretty big and the job of surveying daunting. Luckily you don't need to map the whole thing, just know enough to make good decisions this week.
And honestly, I think for most people, focusing on how to build more human-relevant software is going to be way more helpful to your career than learning about the successor to Docker. But that's just some unsolicited career advice. :)