Docker enables everything to play nicely together. Capsule seems to double down on the old, monoculture way of developing. For people that want to do that, I'm sure your solution is an excellent product. But my own perspective, which may be skewed by being in the bay area, is that those people are the minority, not the majority.
I won't say what you're saying isn't real, but it is happening on a completely different scale than the size of the Java ecosystem. Even on the JVM, what you see as "plenty of Scala" doesn't even amount to 5% -- not that it matters, but it's just an example of why I think your view is skewed.
The size of the Go ecosystem is hardly 1% of that of the JVM (rough estimate), and while Node.js/Python are "a thing" (and are the only languages/platforms of those you mentioned that are used to a substantial amount outside of startups), they are still tiny compared to the use of the JVM. Even in Silicon Valley (which is in itself a very small portion of the software world), the large "webby" application companies (with the notable exception of Facebook) are JVM shops: Amazon, Google, eBay, Twitter, Netflix are either entirely JVM or predominantly JVM, and even Facebook is making growing use of the Java.
Most of the shifts you're seeing is among non-JVM technologies. It's mostly Pythonists that switch to Go and Rubyists that switch to Elixir/Node.js, etc.. The JVM was never the biggest player in the "fast application development" arena -- at the beginning there was VB, and then Perl, and then Python/Ruby and so forth. I see no signs that there is greater movement away from the JVM -- mostly among those who realize they're better served by the "fast dev" platforms even at the cost of performance -- than towards it -- by those realizing they need the best the industry can offer in terms of performance/monitorability/tooling even at the cost of slower development.
I work at a firm where we have dozens of greenfield Spring Boot projects going on.
And if we perform the stats on our public cloud, Java dominates the workload.
Also, remember that Capsule doesn't add another build step. You need to create JARs anyway, so you might as well make them capsules. You then either have the option of adding another step of building Docker images (just because you have some other Docker containers, most of them not even built by you) or not. Capsule just saves you that extra step and still lets you isolate your app in a container if you want, while making everything faster and management+logging easier. I don't think the need/wish to use containers for isolation should dictate your packaging solution.
For most companies that operate several services, having one trusted and strong way to deploy and orchestrate is way more important than an occasional load/build time when working on a new laptop / instance.
Edit: I'm not saying Capsule isn't useful, it just doesn't make any sense to say it compares to Docker, because the use-case is quite different in reality.
...quite a bold statement. Can you cite some sources?
[1]: http://www.zipcodewilmington.com/blog/why-java-skills-matter...
[2]: http://www.infoworld.com/article/2868654/it-jobs/java-develo..., http://www.infoworld.com/article/2608294/java/employers-want...
It's not about philosophy but pragmatism. Most organizations are mostly Java, and even if Java doesn't make up 90% of the components, it makes up 90% of the deployments because that's what the core business software uses. Such organizations get to use a a rather crude tool that takes away some of the power of their technology stack. Why not use a slimmer, faster, less-hassle tool for the majority of your deploys?
And if we want to talk philosophy, Docker really mixes two separate issues -- portable packaging and isolation. Capsule separates them. If you want, you can launch a capsule inside a Docker container. If you want, you can directly launch it in a more convenient container simply by launching it with Shield (or outside a container by running it directly). As Shield will be open-container-compatible, there's no reason why Docker and Shield shouldn't play together. And remember, Capsule requires zero additional tools on top of what developers use anyway (it's just a plain Maven Central library that you stick in your JAR with your build tool).