I'm the initiator of the Flatcar Container Linux project and former CEO of Kinvolk. Thus, I'm rather knowledgeable about the project and was involved in most decisions.
The controversy you speak of is very new to me. If you could point to any references, I'd love to be aware of them.
Firstly, there was nothing "hacked" out of CoreOS. Flatcar is literally the CoreOS Container Linux repos forked and carried on as is. Once the CoreOS EOL was reached we started updating the stale packages. That's it. Any further updates are what any distro would do in the course of maintenance to remain modern and relevant.
Secondly, anything that was previously termed the "Pro" version is now just available in the standard version. So there is no difference. To my knowledge, the project doesn't even produce any Pro versions any longer and I don't think there are even any references to it in our docs. But even when we did have a Pro version, all the work we did was done in the open and was in our source repositories. We just didn't release public builds of those.
Unlike CoreOS, we also developed* and open sourced the update server. It's called Nebraska and available here under an Apache license. https://github.com/kinvolk/nebraska
With regard to a license matrix, you can find all licenses for each release in the respective release directory. For example this one: https://stable.release.flatcar-linux.net/amd64-usr/current/f...
If you do find anything that is not 100% open source, let me know and I'll follow up to make sure that's corrected.
I'm happy your excited about your project. But I think you'll fine it's better in the open source space to compete on merit and form relationships rather than tear down other projects and the work of the people behind the projects.
* based on the Core Roller project: https://github.com/coreroller/coreroller