Wifi seems ok for accessories that feed into an automation system IMO. I'm thinking of weather sensors (light, rain, wind, temp), low fidelity toggle sensors (gate, door, driveway), maybe motion? I don't like devices being wifi unless they have a control at the device in case of network issues (local or cloud). I think my perfect setup would probably be a mesh RF network with sufficient tech to avoid collisions, noise, etc. Having a hub that communicated over wifi/cat5 would be great for extending range from a remote building where no devices would bridge.
That said, zwave/zigbee/insteon (rf) all basically do this already... But, the price is much higher than wifi devices and wifi already works with the broadband people already have. I think sonoff's cheap and hackable design may be partially responsible for the boom (which is a great thing overall).