The simple fact is that WordPress has evolved in to CMS platform. Ghost is aimed at normal bloggers, who just wants to write. Yes, Ghost will bleed some of the users of Wordpress over to them, but it will balance out. Remember how Blogger and WordPress used to be really competitive, some years back? I have tried Ghost, it is good for normal blogging, but when it comes to power users and complex community platforms WordPress takes it all the way. The only drawback which i an see is an impact on WordPress.com, because ".com" WordPress is aimed at bloggers, so with Ghost gaining popularity WP.com will have to up their game play to attract normal bloggers. But when it comes to WP.org, it will continue to grow stronger and evolve in the years to come. Ya, one more thing, who know, ghostavern might also come soon :P