If you are searching for a product in this space, then K8s is the way to go. It has a huge community.
If, on the other hand, you are looking for a small, non-monolithic, resource scheduler + some basic frameworks (i.e. Apache Mesos + Marathon) then DC/OS is not that.
But since Mesosphere are no longer supporting working on Marathon outside of DC/OS, or indeed any framework outside of DC/OS, the Mesos/Marathon is effectively dead, since, while Mesos is open source, the only major supporter of frameworks for it is Mesosphere, and you wont get them unless you use DC/OS.
For some relatively small projects, k8s is sufficient. But pretty quickly you end up needing more and more functionality and you end up in a larger stack like OpenShift.
That's the place that Mesos and DC/OS (IMHO) shine: when you're working with large clusters (1000+) running very different workloads. Because in that scenario, k8s is still pretty immature and you're going to inevitably need to solve all the other problems that OpenShift, DC/OS, Rancher or other stacks solve. Just like Linux distros, in theory, anyone can do it. In practice, it's a pain and you want to pick up a standard distro. That's what these stacks provide: a pre-configured suite of open source tools that get you way more than k8s or Mesos or Marathon on their own provide.
And again, if you are going to be running DC/OS at that scale, then you are going to be running the enterprise version, because you aren't going to be running that much magical shit on million dollar hardware without someone being paid to troubleshoot.
That might be me in a few years, except that Mesosphere seems to be attempting to kill me in the short term by killing non-DC/OS mesos/marathon while crippling non-enterprise DC/OS. So looks like we'll be migrating to K8s and hoping that in a few years K8s scales. The "K8s doesn't scale" argument is losing ground with every new release btw.
Disclaimer: I work at Mesosphere.
Disclaimer: I work for MS
Source: I worked on the team, although we had talked about this at mesoscon in the past.
Of course you are right that in DC/OS there is a lot more besides Mesos that could fail at scale. That is why we are carefully scale-testing DC/OS in its entirety -- under lab conditions (internally) as well as under real-world conditions (large production environments). We will be more transparent about this in the future, but one example I can give is that we regularly run DC/OS on 10^3 nodes for testing purposes.
> if you are going to be running DC/OS at that scale, then you are going to be running the enterprise version
I am not convinced by that argument. Still, just to clarify, Mesosphere Enterprise DC/OS does not have better scaling characteristics than (open) DC/OS. We are trying to land all corresponding goodness in DC/OS.
> killing non-DC/OS mesos/marathon
I understand that brutal decisions have been made. But if you look at Mesos and Marathon as of today (btw., there is no such thing as "non-DC/OS mesos/marathon"), progress is being made at an impressive rate. I observe more "animating" than "killing".
> while crippling non-enterprise DC/OS
I only see additions, no removals. Also, if you were looking at the core technology stack, the delta between Enterprise DC/OS and DC/OS will probably appear to be surprisingly small to you.
> The "K8s doesn't scale" argument is losing ground with every new release btw.
I agree.
The "scale argument" is insignificant compared to other aspects in most of the cases anyway. As we all know :-).
Marathon isn't the only scheduler - Twitter (and some others) have been using Aurora (http://aurora.apache.org/). Currently we are deployed on Mesos/Marathon, and originally I thought Aurora may become more popular because it was Apache "blessed".
(I am a Mesosphere employee.)
I'm afraid I don't know what the plans are for the project (not working on Marathon myself) but being the most popular open source project run and maintained by Mesosphere, I have no doubt that we will continue adding new features and functionality.