We will soon start open sourcing our content management interface, so users have the opportunity to customize the CMS UI to their needs. Most of our customers just want us to take care of the hosting.
In the future, our focus will shift even more to content based BaaS as we will support end user authentication. We are also preparing a new suite of workflow tools that will make managing large datasets a breeze.
"We're going to open source the interface" is a disingenuous answer to the question. Documenting an interface isn't open source. If your plan is "proprietary SaaS", just own it.
Perhaps one of these would serve your needs:
Their software ecosystem is mature as well, as they've been around for a while.
That being said, different genres of software have "known" price points. For source control, it's expensive. For analytics, it's expensive. For blogs, it does seem like the open source model is the only one that's really taken off... Wordpress and Ghost both use the model, and (for better or worse) anchored the price point of blogging software somewhere between free and $10/mo. Makes it hard for any incumbents, which is probably why WordPress still is so popular.
* Of course with "trivial" I meant possible.
That way if you see a traffic spike or a DDoS attack, it's directed only towards static files on S3 and you can let Amazon take care of it. I don't want to be too critical of how people have things set up because I'm sure they have their reasons, but that said I don't think a page request on your site should map directly to an API request to the CMS.
I would have possibly given Directus a spin if it didn't have hard dependencies on the following PHP system extensions: curl, gd, finfo, pdo_mysql and mbstring. Not to go too off topic, but I wish PHP extensions could be installed via Composer and Packagist (similar to how NPM handles native modules).
curl -O https://github.com/directus/directus-docker/blob/master/docker-compose.yml
docker-compose up