I don't think they have to reach the average consumer for this to work. The world is big, and while 99% probably could care less there are more than one reason to own an open source phone. If the lenovo hardware runs Android and Graphene, it's not like they have to make a big investment in it. And the Graphene users could give them some pricing power.

If you are a phone manufacturer looking to differentiate your product, this is cheaper than inventing a display that folds four times or what have you.