I'm not saying its their intent to sell from the onset.
But MS will either make it impossible to compete, or just offer them enough for Google not bother with it anymore.
Companies like Google will always setup a new venture (like an OS division) so that it can be sold off, or so that the parent company cannot be held liable for damages. Its part of business. I would be shocked if this OS is really part of the parent company from the start. They have too much to lose by doing so. Likely it will be a separate entity and be able to be sold off without getting things too complicated for Google.
Except, this is Google we're talking about. Traditionally they don't create projects to sell the operation to other companies. Just about everything they sold off was previously owned by someone else.
This new kernel will probably cover all of their products over time. And since they're creating it from the ground up, they can build it specifically for their needs and avoid any pitfalls in patents or copyright.