I had the same initial reaction, but I think there's good reason to trust the CoreOS folks to remain faithful to the project's goals. Containerization (although foundational) is one part of CoreOS's platform. It's easy to see where the boundaries fall, e.g. I expect systemd and fleetd to keep their respective functionality and not overlap with Rocket.

It become pretty clear once dotCloud became Docker Inc. that they intended to capitalize on the "Docker" brand to sell an integrated orchestration platform. CoreOS already has enterprise customers for their operating system and related components. They seem like the perfect team to take this challenge on.

I think it's also crucial users have more than one viable container option.