I got a $150 aluminum phone with a huge battery, nice enough camera, fingerprint scanner, 3GBs of RAM, expandable storage, etc. etc. ... I don't feel like I need expansion options. What can the higher-specs really offer now a days?
Samsung has the right idea, maybe we'll need better phones for VR. Or maybe built in picoprojectors will be a game changer. But for that you'll need a whole new phone - not just a module snaps on.