WebFWD: What’s an App, Anyway? (blog.webfwd.org)

Just-in-time interaction would be a derivative of the QR culture. The problem however is that no one can afford to leave their camera on constantly to make snapping QR codes a doddle. And that extends further as when leaving your house, the quickest way to save battery is to kill your bluetooth, wifi and even your GPS. Thus while this is a possible future, the issue we have right now is that technology cannot support it. Until we've got phone batteries that can go days without charge (minimal use scenario) and wireless charging in public spaces (the cost of energy is actually increasing), it's an unrealistic and ungrounded hope. Especially for something like a five year vision.