I personally won't consider WiFi an option because I can't control its physical medium. It will remain a nicety, a supplement to my home LAN for convenience, and that's all. I've had enough issues with WiFi at work and at home that I wouldn't want any part of my home automation system to depend on it. As part of a dual-mesh solution, maybe, but not on its own. At 2.4 GHz, all kinds of non-WiFi devices interfere with 802.11g -- microwave ovens, cordless phones, baby monitors, and any other gadgets that use RF and whose manufacturers couldn't or didn't want to go through FCC approval and licensing. People living in apartment complexes often have trouble with this. But even in a house at the end of a dead-end road like mine, it can be an issue.
Faraday cages aside, at one point I had trouble getting data through an access point that was 10 feet away in an open space no matter what channel I used. I borrowed a fancy WiFi spectrum analyzer from work and mapped the signals around my property and discovered that my neighbor across the street was using a 2.4 GHz analog video sender like the ones X10 used to sell. In that case, the bandwidth is so wide that the signal from a single video sender trounces most of the spectrum for digital signals, and WiFi transceivers spend most of their time doing the polite thing and waiting for the interference to subside, which it never does, prior to transmitting. The neighbor wasn't willing to help despite my willingness to buy him a different device, so I had to deal with it. I would have liked to have metal mesh walls on the front of my house at that point. The offending residence had become a rental by that point, and thankfully, that tenant didn't last much longer.
Then there's the issue that adding more WiFi clients effectively reduces available bandwidth exponentially.
802.11ac adds more channels and makes some important changes to the protocol to deal with client density and noise more effectively in some situations, but it doesn't solve the root problem. The move to 5 GHz only buys a little time before other device manufacturers all follow suit as the implementations get cheaper. You can avoid microwave ovens at that frequency but not much else. We just have to hope that the protocol changes make the noise less crippling than it was before. I really do admit that WiFi is an amazing technical accomplishment and I'm awed that it works at all, but I'm not sold on its reliability yet.
At least with PLC, I have a lot more control over what's allowed on the shared physical medium and what's not.
