If they want to turn Ghost into a for-profit company and not a non-profit organization, they can follow in Wordpress’s footsteps exactly: create an open source, non-profit blogging platform, then later create a separate entity (a for-profit company) to offer additional services for money.
But that’s assuming that is their goal. Who’s to say their goal isn’t simply to create a much better blogging experience than Wordpress for the same reason Wordpress was created in the first place (to offer a much better blogging experience than existed at the time)?
I’m all for companies having a business model and focusing on both quality and profit, but that does not preclude the valuable existence of non-profit organizations and open source projects, like jQuery or my own project, Modernizr.
I think a better use of time would be to criticize the obviously for-profit startups that obviously have no business model than an exit strategy of hoping to eventually sell, or get enough users and investment capital to grow to the point where ads become viable.